This exercise helps build the Lats and also works the Triceps (back of the arms).
Steps
Grasp wide grip pull down bar with a wide grip so your hands are on the portion of the bar which curves down.
Stand erect with your abs drawn in. Keeping a slight bend in your elbows and your wrist steady pull the bar down from the starting position to your upper thighs.
With a controlled motion bring the bar back up to starting position.