A DC motor converts direct current (DC) electrical energy into mechanical energy. The most common types rely on the forces produced by magnetic fields. Nearly all types of DC motors have some internal mechanism, either electromechanical or electronic, to periodically change the direction of current in part of the motor. (Adapted from Wikipedia)

When a DC motor is powered, a magnetic field is created in its stator (stationary part of the machine). The field attracts and repels magnets on the rotor (the, rotating part of the machine); this causes the rotor to rotate. (Adapted from iqsdirectory)