Some commands available once you are connected (all IRC commands begin with a forward slash, "/"):

/nick [nickname] - changes your nickname
/whois [nickname] - shows user information for specified nickname
/msg [nickname] [text] - send a private message to specified nickname
/me [text] - performs an action

For more information about IRC visit http://www.irchelp.org/irchelp/altircfaq.html.