If you are looking to turn the sound on and off all you need to do is click on the gear icon at the top right of your game window. This will open up the Settings menu.
From the Settings menu, simply click on the switch below "SOUND" to switch it from "ON" to "OFF".
If you are wondering why there are no game sounds you should check to see if your SOUND is set to OFF. If this does not work, try taking a look in your browser's or computer's sound settings.