1) Find the cable machine and attach a straight bar attachment (if possible the rotating one). Lower the cable pulley to the bottom.
Plant your feet firm on the ground at shoulder width apart with a slight bend in your knees for support.
Make sure the cable pulley is at the top of the cable machine.
2) Grab the bar at wide-grip (wider than shoulder width) with your palms facing down. Arch your back and keep your elbows in front of your hips
3) Exhale as you push down. Make sure that you're only moving your elbows and no other joint. Do not lock your elbows once you reach the bottom of the movement - keep a slight bend.
4) Inhale and bring the weight back to your starting position. Make sure that you control the weight. Raise the weight to where your elbows are barely past 90°.