The ChatApplet communicates with the ChatServer.
Click on the background to move your Avatar sprite around.
Type your text to send messages.
You can choose a different Avatar sprite image from the Options menu.
Resizing your window will automatically resize the background image.
As it currently stands, you can hear from any Avatar that you can see. They may or may not be able to hear you depending on their view. To reduce the number of Avatars that you can hear, reshape your chat frame.