You can do shoulder presses seated or standing up. Let's make these seated. Get comfy -- you're about to work your shoulders off! The main muscle worked are your shoulders, of course. It also affects your triceps.
1) Sit upright at a flat bench and feet flat to the ground.
2) Lower the dumbbells slowly to your shoulders at a 90 degree angle.
3) Then press the dumbbells back up to the starting position.