Motors convert electrical energy into rotational movement.
There are two main classes of motor.
Conventional Motors: These spin in a fairly uncontrolled way. They are useful for propelling vehicles, powering fans or spinning the washing. It is possible to measure how fast the motor is spinning but the exact position of the motor is not generally known. These motors can be any size including huge motors for driving ships or trains.
Google Conventional Motor Images
Stepper Motors: These step through a small known angle so it is possible to know the exact angular position of the motor. They are usually small. They are used for precise movement control in robotics and also in computer printers and disk drives. More ...
Google Stepper Motor Images