/nick
Change your username by typing /nick and the name you want:
/nick ShingujiSakura

/me
Display actions in the room: /me jumps up and down

/msg
Private message someone by either double clicking their username on the list or typing /msg <theirname> hi: /msg ShingujiSakura hi there

A pop-up will ask you yes or no, click yes. It's safe. If the chat doesn't load, you may need to download Java: http://java.sun.com/getjava