What causes a compass to behave as it does?

The needle of a compass is a magnet, and the earth is also a magnet. The side of the compass marked N is attracted to the north pole of the Earth, and the side marked S is attracted to Earth's south pole. The compass will spin to line itself up with the poles it is attracted to. However, if you have other magnets nearby, the compass can spin to line itself up with those instead.