A clutch is that part of the engine which engages or disengages power from the engine crankshaft to transmission. A clutch is the mechanism with the help of which you change gears.
A clutch is made of clutch assembly which includes clutch plate, Clutch centre, Clutch hub, pressure plates, Clutch springs, lever and clutch cable.
In a normal condition a clutch is engaged with the engine. When a rider presses the clutch lever for changing gears, the coil springs in the clutch are compressed and the pressure plate expands which allows the stake of clutch plates to move independently. The stake of clutch is arranged in such a manner that friction plate and steel plate alternate. It makes the engine and clutch to move at different speeds. Ultimately the clutch disengages power to the transmission which allows rider to shift the gears.