Index -> Interface -> Lobby Chat
All lobbies (and many other screens) have their own chat windows. Upon entering a lobby, you automatically join its chat window, and can see any message sent to it.
You can set your preferences for the chat window in the Display and Sound preferences area. You can also change the font size of the text in the chat window by right-clicking inside the window and selecting from the dropdown menu that appears.
To the right of each chat window is a User List showing who is in that lobby.
For more information on Lobby Chat, see:
