How do I send a message or Emote?
You can either click on the left hand side and type or select an Emote. Or you can click on Enter to send a text message or E to select an Emote.
How do I mute the Chat?
You can choose to turn off Emotes, Text Chat or all messaging in the settings of a Party:
Currently, if you have an ongoing game, and then go back to the main menu to mute Emotes or Text Messaging it will only take effect into newly started games and not the ongoing one.
The alternative to this is to mute within an ongoing game: