There is a Tivimate sub to ask questions.

Volume on your device isn't a Tivimate thing, though. It's a device thing. Pair your device with your TV and the volume as well as on/off switch should work (i.e. Firestick, Chromecast, Tivo Stream, Shield, etc.)

Settings.. Remote control

I have the same setup. You have to go into the settings on the Nvidia Shield in order to do that.

Your tv has to support ARC. Most tvs only have one hdmi port that supports it, so make sure you're on the right port.

You will also need a high speed hdmi cable as well.

For more detailed info though, a quick google will get ya going.