The lying leg curl machine specifically targets the calf muscles (gastrocnemius and soleus) and the hamstrings (the biceps femoris, semitendinosus, and semimembranosus muscles).
To start, adjust the position of the leg pad - the pad should rest just below your calves. Then set the height of the pad to around the first hole position on the metal ring. Lie down, with your hips firm against the rest, holding onto the bars at the front. Then lift in a controlled movement up and down, ensuring you do not lock your knees at any point.