The principle of magnets can be analyzed from the molecular structure level of matter:
Matter is mostly composed of molecules, which are composed of atoms, which in turn are composed of nuclei and electrons. Inside the atom, the electrons keep spinning and rotate around the nucleus. Both of these motions of electrons are magnetic. However, in most materials, the direction of electron movement is different, disorderly, and the magnetic effects cancel each other out. Therefore, most substances do not appear magnetic under normal conditions.
Ferromagnetic materials such as iron, cobalt, nickel, or ferrite are different. The electron spins inside them can be arranged spontaneously in a small range to form a spontaneous magnetization region. This spontaneous magnetization region is called a magnetic domain. After the ferromagnetic material is magnetized, the internal magnetic domains are aligned neatly and aligned in the same direction, so that the magnetism is strengthened to form a magnet.
The process of attracting iron to a magnet is the process of magnetizing the iron block. The magnetized iron block and the magnet have different polarities, and the iron block is firmly "sticky" with the magnet. We say that magnets are magnetic.