When you select the Chat you are presented with two options.
To begin a Chat session, choose one of the first two options. You will be presented with a simple interface displaying the participants in a panel on the right and the messages in the central column. At the bottom of the central column, you can type your Chat message.
Type your message into the input field and select Send or Submit (dependant on your interface) and students in the Chat will immediately see what you have sent. They can then reply.
If you want to reply to a student's question, find their name in the Participants list on the right and select Talk. Type your message and select Send.
The message you send is not a private message, it just inserts "To: [name of person]" at the start of your message.
If you think someone is not noticing the messages that are being sent, find their name in the list and select Beep to play a beep noise on their computer and get their attention.
The Themes link enables you to choose between Course Theme, Bubble and Compact views.
If you change the theme after the chat session has begun, you risk losing some or all of the messages that have been sent.