Adjust the machine to your height by adjusting the footpad to allow your knees to be against or below the bottom of the padding. The balls of your feet should be pressed against the footpad, and start with your knees bent and torso straight.
From this kneeling position, extend your knees, tensing your hamstrings to slowly lower yourself down. Once your body is parallel to the ground and your knees are almost fully extended, pause briefly, then squeeze your hamstrings as you bend your knees to bring you back to the starting position. As a regression use a box or the handles to assist yourself getting back to the start position. Maintain a straight back throughout by activating your core. Repeat for the desired amount of repetitions then safely exit the machine.
Avoid using excessive momentum with your back to swing up or drop yourself down or allowing your back to bend throughout the movement.
Fitness for all, for life.