Clutch: Mechanical friction device that engages or disengages the engine from the transmission.
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It is located between the engine and the gearbox. It is used to disengage the engine, which prevents the movement to be transmitted to the gearbox while the gear shifts are made. Roughly speaking, it is the piece that disengages the engine from the wheels when the driver presses on the clutch pedal.
Right after parking my vehicle, it remained with the clutch sunk and there is no way I can possible gear. A green fluid has been spilled. Can anyone please tell me which is the problem?
That is the hydraulic fluid from the clutch pump, which means that your clutch is no longer useful. You will need to change the whole clutch and check whether your flywheel needs to be changed or repaired as well. Do not miss this last point, as sometimes changing the clutch is not enough for the problem to be properly solved.