The process is as follows. The vehicle transmission is placed in either first or second gear, and the clutch is depressed. The key must be in the run position. The car is then rolled forward either by gravity when on a hill or by additional persons or vehicles pushing. Once the car is moving 3-5mph the clutch is engaged abruptly. This causes the movement of the vehicle to drive the engine back through the transmission. This will turn the engine over in much the same way as the starting motor would. Once the engine has started, the clutch can be quickly disengaged to avoid stalling the car, but this is not always necessary.