The clutch system is one of the most essential unit of the car, this makes possible the shifting of gear while the car is about to move or yet moving.
There are two types of clutch systems:
Mechanical clutch system
Hydraulic clutch system
New or the recent vehicles are built with hydraulic systems due to their self adjusting characteristic this is because older mechanical clutches needed frequent adjustment to maintain proper gap between the clutch release bearing and the clutch pressure plate.
http://www.automobileglobe.com/major-components-of-the-clutch-system/