Magnetization is a special kind of energy that certain materials have. It is what causes a material to act like a magnet. Magnets have two sides: a north pole and a south pole, and when you bring two magnets close together, they will stick together because of the magnetization.
Think of the magnetization like a very strong invisible glue that helps glue one magnet to another. This glue is made up of tiny invisible particles called electrons, which are moving and spinning in a certain way. When two magnets are brought close together, these tiny particles interact with each other and cause the magnets to stick together.