That link should bring you to the java-based irc client (A popup window may ask you about cookies or registration or something, accept it)
From there, you input your handle/name and which of the "channels" or "rooms" you want to join.
#swc-members is the main social channel
#swc-traders is obviously the trading channel
#swc-help is obviously the help desk
Just leave the server and port as they are
If you're going to use the chat feature often, you might consider a stand-alone client like GAIM or mIrc to make things easier (You can also then be in multiple channels at the same time)