The Germans borrowed the game from the Greeks and Romans. The gift giving and a lot of other stuff were borrowed from the Christians. The dreidel is spun by one player at a time. Whether he wins or loses depends on which face of the dreidel is up when it falls. Player does nothing.
Player takes everything in the pot.
Player takes half of what is in the pot. Player adds two objects to the pot. When only one object or none is left in the pot, every player adds one. When one person has won everything the game is over.