To enter chat type in a nickname and press connect. If you get in and it tells you that username is taken, you will have to re -enter a new username. Just add some numbers on the end if the username is taken.
Commands!
/nick (Nickname Here) - This is how you change your nickname from within chat.
/me (Message) - This is how you type messages so that you can talk from a 3rd persons view - (Text Appears Red).