Basically, you just put a 'stamp' on a piece of digital paper, which shows what city you are in - then you 'fold' the paper into an airplane and make a little 'throwing' motion with your phone, being careful not to let go and fling your phone across the room, and the plane flies off. Then everyone can make a sweeping motion with your phone to catch other people's planes (seemingly random) to view the stamps, and add your own, then throw it back.
