The answer cannot be limited to a quick reply.
The cause of magnetism is revolution of electrons. A revolving electron acts like a tiny magnet just like a current carrying coil does. If the magnetic moments of all the electrons nullify the effect of each other, it is non magnetic else it is a magnetic substance.
A magnetic substance consists of atoms or molecules having a net magnetic dipole moment. When an external magnetic field is applied or another magnet is brought near, the magnetic dipole moments get aligned and this results in the attraction of the magnetic substance by the magnet.
When the magnetic substance have their dipole moments aligned, it is said to be magnetised.
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