1. Literally, to press the tip of one's thumb and middle finger together and then forcefully slide them apart, producing a snapping sound, often used to attract someone's attention. Tommy, please don't snap your fingers like that at me. If you want my attention, just raise your hand, and I'll come over to you when I have a chance.

2. To make a sudden or impromptu decision that one expects others to adhere to or go along with. So what, you're just going to move around the entire country whenever she snaps her fingers? That doesn't sound like a very equal marriage to me.