It's vital that your engine operates at a proper working temperature. Car engines can get extremely hot and quickly suffer serious damage as a consequence.
Usually located at the front or side of the car behind the fan belt, it's the job of the water pump to squirt water from the radiator to the engine in order to regulate its temperature. Centrifugal force then forces water into the engine block on into the cylinder heads before draining back into the radiator ready to be recycled through the system.
If coolant starts leaking or you notice your engine overheating then replace your water pump immediately, as engine damage may be irreparable.