Top left you see any messagesusers have posted. Note you will only see messagesfrom the time you enter the room until the time you leave the room. To see messages posted when you're not in the room, view the chat logs.
Bottom left is where you can type your messages. Press enter/return on your keyboard to post them to the chat window.
The right panel is the list of users in the room. It shows you how long the user has been idle, and gives you a link to "beep" the user (this will make a beeping sound on their computer if they have sound turned on).
To leave the room, simply close the chat room window.