How do I control my audio and microphone?
From your galaxy’s lobby (the screen you see before entering the galaxy) you can select your microphone and speaker from the Audio Settings section.
When inside your galaxy, you can mute / unmute using the Microphone icon in your action bar at the bottom-left of the screen.
Muted users are signalled with a semi-transparent audio indicator.

Keyboard shortcut: [M] to mute/unmute