Just as you are able to surf the net with a few tricks to help make things easier, IRC is very similar. Below you will find some of the more common IRC commands that we use often.

/join
Type /join #channelname -- to join a channel of your choice
Example: /join #cyprus
What it looks like:
 
[18:44] *** Now talking in #Cyprus
--Op-- mad-boy has joined the channel
[18:44] *** Topic is 'Welcome to #Cyprus and Enjoy your stay ! Visit us at www.cyprusirc.net'
[18:44] *** Set by stevez on Sun Jul 23 16:10:34

/me
The /me is an action message.
Type /me 'does anything'
Example: /me waves hello
What it looks like:
* mad-boy waves hello

/msg
Type /msg nickname (message) to start a private chat.
Example: /msg dem` Hey dem, how are you?
What it looks like:
-> *puddytat* Hey tat, how are you?

/nick
/nick changes your nickname
Example: type /nick newnickname (limit 9 characters)
What it looks like: I typed /nick mad-AWAY
*** mad-boy is now known as mad-AWAY

/notice
A notice is used to send a short message to another person without opening up a private window.
Type /notice nickname (message)
Example: /notice badnick Please change your nickname for this family channel.
What it looks like:
-> -badnick- Please change your nickname for this family channel.
 
/part
Type /part -- to leave one channel
Type /partall -- to leave all the channels you are in

/ping
Type /ping nickname. What this command does is give you the ping time, or lag time, between you and the person you pinged. Lag can be explained as the amount of time it takes for you to type your message and for others to read your messages. Unfortunately, lag is always a part of IRC, although most times it's not a problem, just a nuisance.
Example: /ping dem`
What it looks like:
[19:04] -> [dem`] PING
[19:04] [dem` PING reply]: 0secs

/query
Similar to the /msg, except it forces a window to pop open.
Type /query nickname (message)
Example: /query AndreasC Sooo....what's new?
What it looks like:
<mad-boy> soooo....what's new?

/quit
Type /quit to leave IRC altogether. This disconnects mirc from the server.
Example: /quit Going out for dinner...nite all
What it looks like:
*** Quits: mad-boy (Going out for dinner...nite all )

/ignore
Unfortunately, there will be times when you don't want to talk to someone, or else someone may be harassing you.
By typing /ignore nickname 3, you will not receive anymore messages from that person.
Example: /ignore WestMan 3
To Unignore them, type /ignore -r WestMan 3
What it looks like:
*** Added *!*west@*.cytanet.com.cy to ignore list
*** Removed *!*west@*.cytanet.com.cy from ignore list

/whois
Type /whois nickname to see a bit more information about another user. You'll see what server another person is using, or what their ISP is. Pretty helpful when you don't recognize a nickname that wants to chat. You may recognize the IP, (Internet Protocol) and then feel more comfortable carrying on a conversation. You'll also be able to see what other channels a person is in, which might be a good indicator if you really want to talk with them or not.
Example: /whois mad-boy
What it looks like:
mad-boy is mad-boy@mad-boy.org * www.NetSmart.com.cy
mad-boy on @#Cyprus
mad-boy using Mesa.AZ.US.Undernet.Org USeNet Leader!
mad-boy has been idle 18secs, signed on Sun Jul 23 18:47:26
mad-boy End of /WHOIS list.

/chat
This opens up a DCC/CHAT window to another user. What's nice about these is that you can continue to chat even if you get disconnected from your server.
Word of Caution: Do NOT accept dcc/chats nor dcc/gets from anyone that you don't know.
Type /chat nickname.
Example: /chat dem`
What it looks like:
Chat with dem`
Waiting for acknowledgement...

/help
There's one more very helpful command, and probably the one you'll use a lot when first starting out. In fact, I still use it quite a lot, and that's the built-in help menu of mIRC.
Type /help, you'll see the the mIRC Help Menu open up. You can do a search from there, or you can type /help topic. Either way, a TON of information at your fingertips.
Example: /help Basic IRC Commands
 

Quick Command Reference Guide

/ Recalls the previous command entered in the current window.
/! Recalls the last command typed in any window.
/action <action text> Sends the specifed action to the active channel or query window.
/add [-apuce] <filename.ini> Loads aliases, popups, users, commands, and events.
/alias <alias name><command(s)> Adds the given alias to the Tools/Aliases list.
/ame <action text>Sends the specifed action to all channels which you are currently on.
/amsg <text> Sends the specifed message to all channels which you are currently on.
/auser [-a] <level><nick|address> Adds a user with the specified access level to the remote users list.
/auto [-r] [on|off|nickname[ type]|address] Adds <-r removes>auto-opping of a nick or address or sets it on or off totally. The type determines the used address syntax.
/away <away message> Sets you away leave a message explaining that you are not currently paying attention to IRC.
/away Sets you being back.
/ban [#channel] <nickname>[type] Bans the specified nick from the curent or given channel.
/beep [
/channel Pops up the channel central window <only works in a channel)
/clear [nickname|channel] Clears the entire scrollback buffer of the <given>window.
/clearall Clears all text in all open windows.
/close -icfgms [nick1] [nickN] closes inactive, chat, fserve, get, message or send windows.
/closemsg <nickname> Closes the query window you have open to the specified nick.
/creq [ask | auto | ignore] Sets your DCC 'On Chat request' settings in DCC/Options.
/ctcp <nickname><ping|finger|version|time|userinfo|clientinfo> Does the given ctcp request on nickname.
/ctcpreply <nickname><ctcp>[message] Sends a ctcp reply message to nickname.
/ctcps [on|off] Sets the Tools/Remote/Commands setion on or off or checks its status.
/dcc send <nickname>[file1] [file2] [file3] ... [fileN] Sends the specified file(s>to nick.
/dcc chat <nickname> Opens a dcc window and sends a dcc chat request to nickname.
/dde [-r] <service><topic><item [data] Allows DDE control between mIRC and other applications.
/ddeserver [[on [service name] | off] To turn on the DDE server mode, eventually with a givem service name.
/describe <#channel><action text> Sends the specifed action to the specified channel window.
/disable <#groupname> De-activates a group of commands or events in the remote section.
/disconnect Forces a hard and immediate disconnect from your IRC server. Use it with care.
/dlevel <level> Changes the default user level in the remote section.
/dns <nickname | IP address | IP name> Uses your providers DNS to resolve an IP address.
/echo [N] <-s|a|[=]nickname|#channel> <text> Displays the given text only to YOU on the given place <status, active window, query or channel>in color N.
/enable <#groupname> Activates a group of commands or events.
/events [on|off] Shows the Tools/Remote/Events section status or sets it to listening or not.
/exit Forces mIRC to shutdown and close.
/finger <nickname | address> Does a finger on a users address... also if his nick is given.
/flood [
/flush [levels] Clears all nicknames from the Remote/users list that are currently not on your channels.
/flushini <filename> Forces the specified INI file to be saved to disk.
/font Activates the font selection dialog.
/fsend [on|off] Shows fsends status and allows you to turn dcc fast send on or off.
/fserve <nickname><maxgets><homedirectory>[welcome text file] Opens a fileserver.
/groups [-e|d] Shows all <enabled or disabled>groups defined in the remote sections.
/guser [-a] <level><nick>[type] Adds the user to the user list with the specified level and address type.
/help <keyword> Brings up the Basic IRC Commands section in the mIRC help file.
/ial [on|off] Turns the Internal Address List on and off.
/identd [on|off] [userid] Activates the IdentD server with the given usedid.
/ignore [-rpcntiu#][on|off|nickname|address] [type] Ignores a nick or address or sets ignore on or off totally. -r to remove.
/invite <nickname><#channel> Invites another user to a channel.
/join <#channel> Makes you join the specified channel.
/kick <#channel><nickname> Kicks nickname off a given channel.
/links Shows the entire list of IRC servers in the network you are currently connected to.
/list [#string] [-min #] [-max #] Lists all currently available channels, evt. filtering for parameters.
/load <-a|p
/loadbuf [lines] <window><filename> Loads lines from a text file into the specified window. <like echo)
/log [on|off] [windowname] Shows the logging status or sets it on or off for the window.
/me <action text> Sends the specifed action to the active channel or query window.
/mode <#channel|nickname>[[+|-]modechars [parameters]] Sets channel or user modes.
/msg <#channel|nickname><message> Send a private message to this user without opening a query window.
/names <#channel> Shows the nicks of all people on the given channel.
/nick <new nickname> Changes your nickname to whatever you like.
/notice <nick><message> Send the specified notice message to the nick.
/notify [-sh][-ar][on|off|nickname] Toggles notifying you of a nick on IRC or sets it on or off totally.
/onotice [#channel] <message> Send the specified notice message to all channel ops.
/omsg [#channel] <message> Send the specified message to all ops on a channel.
/part <#channel><message> Makes you leave the specified channel.
/partall <message> Makes you leave all channels you are on.
/perform [on|off] Toggles the File/Options/Perform <on startup>section.
/play [-cp q# m# rl# t#] [channel/nick] <filename>[delay|linenumber] Allows you to play text files to a channel. Read the help !
/pop <delay>[#channel] <nickname> Performs a randomly delayed +o on a not already opped nick.
/protect [-ar][on|off|nickname|address] Toggles protection of a nick or address or sets it on or off totally.
/query <nickname><message> Open a query window to this user and send them the private message.
/quit [reason] Disconnect you from IRC with the optional byebye message.
/quote [-q] <raw command> Sends any raw command you supply directly to the server. Use it with care !
/raw [-q] <raw command> Sends any raw command you supply directly to the server. Use it with care !
/remote [on|off] Sets the entire Tools/Remote setion on or off or checks its status.
/remove <c:\path\filename> Will delete the requested file.
/rlevel <access level> Removes all users from the remote users list with the specified access level.
/run <c:\path\program.exe> [parameters] Runs the specified program, evt. with parameters.
/ruser [-r] <nick[!]|address> [type] Removes the user from the remote users list.
/save [-apuce] <filename.ini> Saves remote sections into a specified INI file.
/savebuf [lines] <window> <filename> Saves lines from the buffer of a window to a file.
/say <text> Says whatever you want to the active window.
/server [server # | server address [port] [password]] <Re)connects to the server or a newly specified one.
/sound [nickname|#channel] <filename.wav> <action text> Sends an action and a fitting sound request.
/speak <text> Uses the external text to speech program Monologue to speak up the text.
/splay <c:\path\filename.ext> Plays .wav and .mid files to you. (like /wavplay)
/sreq [ask | auto | ignore] Sets your DCC 'On Send request' settings in DCC/Options.
/strip [+-burc] Turns removal of color codes <see Options dialog>on/off.
/time Tells you the time on the server you use.
/timer[N] <repetitions> <interval in seconds> <command> [| <more commands>] Activates a timer.
/timestamp [-a|e|s] [on|off] [window] For Turning on/off timestamping in windows or globally. <-s = for status window, -a = for active window, -e = for every window)
/titlebar <text> Sets mIRC's titlebar to the specified text.
/topic <#channel> <newtopic> Changes the topic for the specified channel.
/ulist [<|>]
/unload <-a|-rs> <filename> This unloads the specified alias or remote script file.
/url [-d|on|off|hide] Opens or closes the URL window that allows you to surf the www parallel to IRC.
/uwho [nick] Pops up the user central with information about the specified user.
/version Tells you the version of the IRC server you use.
/wavplay <c:\path\filename.ext> Locally plays the specified wave or midi file.
/who <#channel> Shows the nicks of all people on the given channel.
/who <*address.string*> Shows all people on IRC with a matching address.
/whois <nickname> Shows information about someone in the status window.
/whowas <nickname> Shows information about someone who -just- left IRC.
/window This allows you to create and manipulate custom windows.
/write [-cidls] <filename> [text] To write the specified text to a .txt file.
/writeini <inifile> <section> <item> <value> To write to an .ini file.
 

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A new feature in mIRC allows you to minimize mIRC and lock it with a password for strange eyes. If you control-minimize mIRC (keep the Ctrl-key pressed down while minimizing mIRC), it will be locked with your password. If no password was set previously mIRC will ask you for one. Later when you want to maximize mIRC you need your password to activate it. An extention of this feature in the /File/Options/General/Lock/ menu can be used to lock mIRC or certain channels for your children! Previous Tips (Become a mIRC Wizzard).

Shift+Mouse on Switchbar - Did you know that you can 'fast-close' a window in mIRC by clicking its button on the Switchbar while holding the SHIFT key pressed down??

/uwho - Ever wondered who you're actually speaking with? The /whois {nick} command shows you a lot of cryptic info in the Status window but the /uwho {nick} command will open a clear and informative User Central. Give it a try! You can also store address info of your friends in the User Central for future reference.

ALT + Minus - Press the key combination ALT and 'minus' simultaneous to access the windows' System Menu's (found under that little horizontal bar in every top left corner of ANY window in mIRC and windows). Here you can set the fonts you like, the logging options, save the buffer and set various other things for private and channel conversations.

/clear - Use the /clear command to flush away all old text you dont want to read again. /clearall clears all text in all windows!

Doskey - Remember that old doskey feature under DOS? mIRC has it too :-) Use the arrow up/down keys, eventually combined with SHIFT, to recall old commands and text lines.

/channel - The /channel command will open the Channel Central that displays all modes and bans set on your current channel.

/pdcc - Use the undocumented /pdcc {bytes} command to speed up your DCC sessions! It will pump your data packages away to the reciever, ahead of the confirmation of arrival. Try it, it works :-) Something like /pdcc 20000 will do fine.