Now you can go ahead and chat with the folks in the room. The list of people in the room is in the upper right panel of the window. To type a message, place the cursor in the text input panel at the bottom of the screen (the short, wide rectangle with the cartoon balloons to the right), type a message, and hit the Enter key on your keyboard.
To choose a particular expression, use the emotion wheel under the self-view of your character in the lower right-hand portion of the window. To whisper a message to just one person, select them in the upper right hand panel, enter the message, and press the whisper balloon button - the dashed balloon in the middle of the balloon icons, to the right of the text entry panel.