Primary muscles are the rear delts (back of the shoulders), secondary are upper back and traps.

Grab the single handle from the lower pulley. Stand with your feet shoulder width apart and lean over until your back is almost parallel to the ground.

Keep your elbow slightly bent, holding the handle in front of you. Raise your hand until it is a little higher than your shoulder and lower slowly. Repeat until you have finished the set. Repeat with your other arm when you have finished your reps.