This movement is used to build mass and thickness in the back. It is also a great strength builder for the back.
Begin by placing your feet on the platform and lay face down on the machine; your chest should be on the pad. Reach down and grab the handles with a double overhand grip or your palms facing down. Lift the bar off the rack and allow your arms to hang in a fully extended position. Now, pull the bar towards your chest by driving your elbows back. Do not swing the weight or allow your upper body to come off of the chest pad. Fully contract your back muscles at the top position and then slowly return the weight back to the starting position. Repeat this movement until your set is complete.
Keep your elbows tight to your body so that the focus of the movement remains on your back muscles.
You can change your grip to work your back muscles differently; you can use palms up grip, which will work your biceps more. Also, depending on the machine, you may be able to use a neutral grip, or palms facing together.