The big idea
A magnet produces a magnetic field, a region around it where it pushes or pulls on other magnets and on some metals. Magnets hold notes on fridges, spin the motors in fans and cars, make the sound in headphones and point compass needles north.
How it works
Only a few materials are magnetic materials, meaning a magnet attracts them: iron, nickel and cobalt, and alloys containing them, such as steel. Aluminium, copper, gold and most other metals are not.
Every magnet has two poles, north and south. Like poles (N and N, or S and S) repel; unlike poles (N and S) attract. If you cut a magnet in half, you don't get a separate north and south: you get two smaller magnets, each with both poles.
We draw the field with magnetic field lines. They point the way a compass needle's north end would point. Outside the magnet they run from the north pole round to the south pole, and they bunch up where the field is strongest, at the poles.