How does magnetism work?
BLUF: Magnetism is a force created by moving electric charge. Inside atoms, electrons act like tiny spinning magnets; when many align in the same direction, their fields combine into the push or pull we can feel.
It is one strand of a single fundamental interaction, and, unified with electricity, it powers everything from compasses and motors to hard drives and MRI machines.
Tiny magnets inside atoms
Magnetism begins with electric charge in motion. Every electron carries a property called spin, plus orbital motion around the nucleus, and both make it behave like a minuscule bar magnet with a north and a south pole. In most materials these tiny magnets point in random directions and cancel out. In iron, nickel, and cobalt, quantum effects lock neighboring electron spins into parallel alignment, forming regions called domains. Stroke such a metal with a magnet, or cool it in a strong field, and the domains line up together. Their fields then add into a single, macroscopic magnetic field that can grip a paperclip or deflect a compass needle. Break the magnet in half and each piece keeps both poles; you never isolate a lone north or south.
One force: electromagnetism
The deeper truth is that magnetism and electricity are two faces of one force. In 1820 Hans Christian Orsted noticed a compass needle twitch beside a current-carrying wire: moving charge creates a magnetic field. A decade later Michael Faraday showed the reverse, that a changing magnetic field drives an electric current. In the 1860s James Clerk Maxwell knit these observations into a set of equations describing a single electromagnetic field, and predicted that light itself is a self-propagating electromagnetic wave. Einstein went further: magnetism is largely what the electric force looks like from a moving frame of reference, a consequence of special relativity. So there are not really separate electric and magnetic forces, only electromagnetism, viewed from different vantage points and different states of motion.
Where magnetism shows up
Electromagnetism runs modern life. Every electric motor and generator exploits the link between current and field, converting electricity into spinning motion or motion back into electricity, turning fans, cars, and power-plant turbines. Hard drives and credit-card strips store data as patterns of magnetized grains. Loudspeakers and microphones translate between electrical signals and sound using coils and magnets. MRI scanners use powerful superconducting magnets to image soft tissue, and maglev trains ride on magnetic forces. On the largest scale, Earth behaves like a giant magnet: convecting molten iron in its outer core generates a field that swings compass needles and helps shield the planet from harmful solar particles. Even the auroras are charged particles funneled along that field toward the poles.
Common misconceptions
Myth: all metals are magnetic. Reality: only ferromagnetic metals such as iron, nickel, and cobalt are strongly attracted; aluminum, copper, and gold are not. Myth: a magnet holds a limitless supply of free energy. Reality: a static magnet does no net work, and any lifting energy comes from whoever moves the object. Myth: a compass points to Earth's magnetic north pole. Reality: a compass needle is drawn to what is physically a magnetic south pole, which happens to sit near the geographic north. Myth: magnets last forever. Reality: heating above the Curie temperature, sharp blows, or strong opposing fields can scramble the domains and demagnetize a magnet.