In a manual transmission car, the clutch controls the connection between the shaft coming from the engine and the shafts which turn the wheels. It is a vital part of the car´s working machinery as the engine generates power all the time, and has parts which are constantly rotating, but the wheels are not constantly spinning. To allow the car to both change speed and to come to a complete stop without turning off the engine, the connection between the wheels and the engine needs to be temporarily broken.
There are two main parts to your clutch: the clutch plate and the flywheel. If your foot is not pressing down on the clutch pedal, there are a set of springs which keep a pressure plate pushed up against the clutch plate. The pressure from the springs also pushes the clutch plate up against the fly wheel. This connects the engine to the shaft which transfers motion to the wheels, and makes the two turn at the same time. When your foot pushes down on the clutch pedal, you press down on a release fork, which, through a series of springs and pins, pulls the pressure plate away from the clutch plate. This breaks the connection between the rotating engine and the wheels, meaning that the wheels continue to spin but under their own momentum, not through the power of the engine. This design allows you to disengage the wheels from the engine in order to change gear, allowing drivers to have a great amount of control over the speed of their car.