In a restaurant in the USA, it’s usually enough to just make eye contact with the waiter — the service is that good. If the waiter doesn’t see us, the next step would be to simply raise a hand while looking at the waiter. If necessary, we might say “excuse, me, waiter”. In the US, it would be extremely rude to clap one’s hands or snap one’s fingers (it’s possible they do that in parts of Europe).
If you’re with your friends, then you can generally snap, clap or do anything you want.