Magnetism is the phenomenon by which some materials attract other materials like iron.
Certain materials possess that ability to attract metals like Iron. They are called magnets. The force is called magnetic force.
In atoms present in materials, there are nucleus and electrons. The electrons have spin and orientation. When substance is not magnetized, the rotations of electrons have random directions. So the attraction force due to one cancels the attraction force due to another.
In some substances, the atoms and the electrons are oriented in a particular direction. So their magnetic/attraction force is added. Thus they are able to attract other materials like iron. In Iron, the electrons can be easily magnetized into aligning along one direction.
Natural magnets have their atoms and molecules aligned already. Some ferromagnetic materials can be magnetized by the movement of magnets on their surface, many times in the same direction.