I (Gym Professor) will try to avoid my usual trick of waffling too much, but you really should understand the action of each muscle and it's relationship with others. This is important to perform the exercise correctly and help avoid possible injury. You should review the kinesiology (human movement) section. Also, you may find the sample gym workout routines of benefit, see 'Workouts' category. If that's not enough, remember we offer a free-to-download workout app (GP Shuffle) including step-by-step exercise demonstrations.
Below are a list of various shoulder exercises. The exercise pages will provide basic instruction and detail muscles exercised, what the exercise is for, and who the exercise is for. Over time, I'll also include Youtube video's for the more commonly performed gym exercises, to better demonstrate the weight training exercise being performed.
If you have a shoulder injury (most likely Rotator Cuff related) and find exercises such as Flat Bench Press, Shoulder Press etc. uncomfortable, you really should try GLOBE GRIPZ™.