Check out this Roll20 macro tutorial. The information on the Roll20 Wiki is also pretty informative. If you have Google Hangouts setup, that's basically all you need to do with it. A link will be provided in game for voice chat. All you need to do is click that to join the call. You can mute audio or video with microphone and camera icons that show up in the top of the call when you join. If your mic or speakers aren't working right, you can click on the gear that will be in the same toolbar to switch the input and output of them.