How do I turn the sound on/off?

If you are looking to turn the sound on and off all you need to do is click on the speaker icon at the top right of your game window. This will affect all the sounds in the lobby and in the games themselves. 

If you are wondering why there are no game sounds you should check the speaker icon to see if your sounds are disabled. If this does not work, try taking a look in the computer's speaker options.