Base IRC Commands:
/nick
/nick changes your nickname
Example: /nick newnickname (limit 9 characters)

/msg
/msg nickname nickname (message) to start a private chat..
Example: /msg puddytat Hey tat, how are you?

/quit
/quit to leave IRC altogether. This disconnects irc from the server.
Example: /quit Going out for dinner...nite all!

More information in: http://www.ircbeginner.com/ircinfo/ircc-commands.html