To perform the experiment you need a needle, straw, water bowl, a magnet (neodymium may be). Rub the same page on the magnet needle, always in the same direction. Then the straw make two floats. Put the needle floats on the water, notice that the needle begins to turn. I stop always pointing the same direction.

Explanation
The compass is an instrument used for situational awareness. The Earth's magnetic field affects the magnetic needle compass, so that it always shows the direction of magnetic north pole.