A DC motor works by converting DC power into mechanical energy using the principle that a current-carrying conductor placed in a magnetic field experiences a mechanical force. It has a field system including field windings that generate a magnetic field, an armature with windings on a core, and a commutator that redirects current flow to keep the torque moving the motor. The speed of a DC motor can be controlled by changing the current through the field windings to adjust the magnetic flux or by changing the armature resistance to vary the voltage applied to the armature. Common DC motor types include shunt, series, and compound motors used in various applications like fans, pumps, machine tools, locomotives, and industrial equipment.