This exercise combines a Hammer Curl with a Preacher bench.
Adjust the seat of the bench so your arms are level with the top of the bench. Grasp a dumbbell in each hand with your palms facing each other, shoulder width apart and extend your arms fully along the bench. Keeping your arms and elbows on the bench at all times, curl the dumbbells up towards your head. Pause for a moment and then lower the bar back to starting position.
Perform this exercise in a slow controlled manner for best results.