Diamagnetism is when materials weakly repel magnetic objects when a magnetic force is applied to them. Paramagnetic objects will briefly align with a magnetic force, but return to their usual state when the magnetic force is removed. Ferromagnetism occurs when the magnetic forces in an object will align with a magnetic field when it is applied, and then continue to stay aligned when the forces are removed.
Diamagnetism occurs when the atoms in a material align so that they oppose any magnetic force that is applied to them. This means that the object will repel any magnet. Diamagnetism is the standard state when objects are not paramagnetic or ferromagnetic, which means that most objects are diamagnetic.
Paramagnetism occurs when the magnetic fields produced within an object by the electrons in its atoms do not fully cancel each other out. This means that when a magnetic force is applied to paramagnetic objects, they will become magnetic in a degree that is equal to the force that is applied. If the magnetic force that is applied is small, these objects will become only slightly magnetic. If a greater force is applied, these objects will become more magnetic.
Ferromagnetism is when the atoms in a metal line up into sections known as domains, which individually have strong magnetic charges. The object as a whole does not have a magnetic charge, however, because these domains are randomly organized and cancel each other out. When a magnetic force is applied, these domains will line up and become strongly magnetized. Ferromagnets are characterized by their magnetic retention after the magnetic field is removed.