The gas key is on top of the bolt carrier. It's the tube looking thing that is bolted on top. If that's loose, and gas leaks at the joint between the carrier and the key itself, it can cause problems.
The gas rings are on the bolt itself, on the end that lives inside the bolt carrier. Take the bolt carrier apart, and pull the bolt out. You'll see them, there are three of them...or at least there should be. Post pics, if you can, as well (of everything, not just the bolt)
He was talking about a Magpul B.A.D. (Battery Assist Device) lever. It's thing that bolts onto your bolt catch so you can activate it with your index finger in the trigger guard. Their only purpose is to look cool, and cause malfunctions