This is a great shoulder exercise. Shoulders are important for a great looking back and arms.
Sit on the edge of a bench with your knees hip width apart. Hold a dumbbell in each hand. Hold the weights in front of your shoulders, palms facing your body. As you press the dumbbells overhead, rotate you wrists and elbows so your palms face out at the top. Return along the same path. Use weights that allow you to fatigue around rep 8-15. Do 3 sets of this move.
Here is an instructional video.