I've just downloaded, now I want to finger bang with people. the problem is, how do I ask them?
Try being honest and direct! "Hey, would you like to Finger Bang?" is clear* and to the point. If someone says "no", that's ok! There's plenty of people out there that would love to Finger Bang with you!
*In all seriousness though, you should mention that it's a game. Please don't just ask random people to Finger Bang without context.