Invisible reach
Hold a magnet near a paperclip and the clip jumps before they touch. Something is acting across the gap. That something is the magnet’s field: a region of influence that fills the space around it, strongest close to the magnet and fading quickly with distance.
You cannot see a field directly. You can only see what it does. Sprinkle iron filings around a magnet and each one turns to line up with the field where it sits, and together they trace its shape.
Two ends, always
Every magnet has two poles, called north and south. The field is strongest at the poles and weakest around the middle. Cut a magnet in half and you do not get a north half and a south half: you get two smaller magnets, each with both poles. Nobody has ever found a pole on its own.
The rule for two magnets is short. Opposite poles attract; like poles repel. North pulls south toward it and pushes another north away.
Try it: choose N facing S and set the distance to Close. Then choose N facing N at the same distance and compare how the lines bend.
Lines that never cross
The scene draws the field as field lines. They run out of the north pole, curve around through the space outside the magnet, and back into the south pole. Where the lines are packed closely the field is strong; where they spread out it is weak. Lines never cross, because at any one point the field can only point one way.
When two magnets face north to south, their lines join up into a single pattern that runs straight from one to the other. When they face north to north, the lines from each magnet bend away from the other, and the gap between them empties out. The pattern in the space is the push or the pull, made visible.
What responds, and what does not
A magnet attracts iron, nickel and cobalt, and steel because it is mostly iron. It does nothing to wood, glass, aluminium or copper. The difference is inside the atoms: in a few metals the atoms are themselves tiny magnets, and a field nearby lines them up so that the whole piece becomes a magnet for as long as the field is there. That is why a paperclip clings to a magnet and can pick up another clip while it does.
The planet is a magnet
The Earth has a field of its own, produced by currents of molten iron churning far below the surface. It is weak by fridge-magnet standards, but it reaches thousands of kilometres into space. A compass needle is a small magnet free to turn, and it swings to line up with that field, which is how sailors found their way for a thousand years before satellites. The same field steers charged particles from the Sun toward the poles, where they light the sky as auroras.