When you think about your shoulder, what comes to mind are the deltoid muscles. You have a front deltoid, middle deltoid, and a rear deltoid to keep things simple. Each take different exercises to hit the spot. This muscle begins at your neck trapezius region and ends close to your upper lats, bicep and tricep. There is also the rotator cuff.
Exercises for mass:
Front Raises
Lateral Raises
Bent-Over Lateral Raises
Arnold Presses
Military Presses
Upright Rows
Rocky Press