As a car’s engine operates, it generates high temperatures within the motor. This heat must be handled appropriately, and the motor kept cooled at a proper operating temperature range, or the vehicle will suffer potentially catastrophic failure…you’ll blow it up. Generally, a vehicle’s water pump, driven by the motor via the timing belt (or serpentine belt in some models), circulates the coolant/antifreeze around the “water jacket” of the motor, and back through the radiator thus cooling it. It also facilitates circulating coolant/antifreeze through the heater core of the car, so you can stay warm in the winter.