Guests can't game chat, but FICS membership is free and when connected as a guest, a signup link displays in console on connection. This link can be long pressed on iOS or long clicked on Mac.
Chat must be unlocked first which is simple. Just click the agree to EULA in Main View and accept the server policy on behavior which is basicaly keep it clean and nothing abusive. Later if the user wants, they can lock chat in settings again, and play in silence. If chat is unlocked after a game, all messages in consoles not shown will show.
When the board is showing a game that the user is playing, examining or observing, the Actions menu will have an option for members to tell Opponent if playing, Whisper to other observers if observing or kibitz to everyone on the board if examining.
Also the command say can be used to chat with opponent or last opponent. For example type say thanks for game. To have all says go to both Main View and Board Console, choose the Says in Main setting in top Console area of settings.
Mac users also have a command mode typing area below the board console and can use the say command here if this is quicker than going through the Actions menu.