Why do magnets attract and repel?

Magnetism arises from the movement and spin of electrons, each of which acts like a tiny magnet. In most materials these atomic magnets point in random directions and cancel out, but in ferromagnetic metals like iron, nickel, and cobalt, groups of atoms called magnetic domains can line up so their fields add together, producing a strong overall magnet. Every magnet has a north and a south pole, and the field lines run from north to south. When you bring two magnets together, opposite poles (north to south) attract because their field lines join smoothly, while like poles (north to north) repel because their fields oppose one another. Earth itself behaves like a giant magnet, generated by the churning of molten iron in its core, which is why a compass needle swings to point roughly north.