The clutch allows to connect and disconnect the engine and the transmission while starting up and during shifts. Friction plates route the rotation of the engine crankshaft to the gears, and then to the wheels. It takes the rotation up slowly, so that you aren’t off to a screeching start. In a manual transmission, the clutch is disengaged when you press the pedal down. The pedal works the thrust pad, and it presses levers in the middle of the clutch cover. Clutches are useful in devices with two rotating shafts. In these devices, one of the shafts is typically driven by a motor or pulley, and the other shaft is driving another device. In a drill, for instance, one shaft is driven by a motor and the other is driving a drill chuck. The clutch connects the two shafts so that they can either be locked together and spin at the same speed, or be decoupled and spin at different speeds. Doing all this lifts the pressure plate away from the clutch plate. The flywheel (which is turned by the crankshaft from the transmission shaft) gets disconnected. When you lift the clutch pedal, springs force the pressure plate and clutch plate against the flywheel. The clutch plate friction linings allow it to slide before becoming engaged. The sliding causes a smooth start instead of a jolt.