DC motors are internally commutated DC motors (motor current direction is changed internally by a brush). These motors are designed to be used with a DC power source. DC motors consist of an armature and a permanent magnet. When current passes through the coil on the armature, a force is created due to the magnetic effect of the permanent magnet. While the armature is moving the brush of the motor changes the direction of the current mechanically, causing the shaft of the motor rotating continually.
DC motors are the first commercial electric motors used to lift mechanical weights. DC distribution systems are used for around 100 years for controlling DC motors in industrial and commercial buildings.
DC motor speed can be adjusted by controlling the voltage or the magnetic power applied. Therefore setting the connections accordingly between the motor and its source the torque and power characteristics of the motor can be controlled. This setting can be used to rotate the motor with a fixed speed or variable speed depending on its load.
DC motors are not common in power electronics because they need maintenance when their brushes are deformed and needs replacement. In these applications brushless DC motors are more frequently preferred. Commutation of these motors is handled electronically.
Learn more about DC Motors - What is a DC Motor