Electromagnetism studies theaffects of electric charges both at rest and in motion. As one of the four fundamental forces of nature and the main binding force of the atom outside the nucleus, electromagnetic theory is important to understanding nature.
The property of subatomic particle that gives rise to electric fields is called charge. The charge of a particle can be negative, positive, or neutral. Charge is a fundamental property of matter. Magnetism is the force of attraction or repulsion resulting from the motion of electric charges.
While the force lines associated with electric charges tend to be strait, magnetic force lines tend to be circular. Electrodynamics is the branch of physics dealing with the electromagnetic forces between electric charges. In its most basic form electrodynamics deals with the affect of charges in relative motion. It is this mutual production of electric and magnetic fields that forms the bases of the unification of eclectic and magnetic fields. Every thing else in electromagnetism extends from this starting principles.