As always, check with the doctor to make sure these exercises are right for you and your problem.  These exercises are usually  prescribed at different points in the rehabilitation for different problems.

The Big 3 is a high repetition, low weight exercise to help build muscle endurance and quite specifically are engineered to make the rotator cuff stronger. They are very shoulder friendly and are designed to strengthen muscles more comfortably. By slowly increasing the demand on the muscles over a longer period of time and positioning the arm at lower heights, the Big 3 program is less likely to aggravate common shoulder problems.  Do these exercises once per day.  If you are really getting sore, you  are doing too much. The key to these exercises is to do them frequently, a little at a time.  Start by doing these with 20 repetitions for each exercise.  As you get better, do two sets of 20.  Eventually move up to 3 sets of 20.  If this gets too easy, come to the office and get a tougher sportscord.  If that's too easy, increase to sets of 30.

Place the cord around a doorknob or in the door as shown, grasp the handle and position your self perpendicular to the sport cord as shown below. Keep your elbow against your side and pull out against the cord.

Turn around and face the opposite direction. Position yourself perpendicular to the sport cord – only this time you will be pulling in against the cord. Once again, keep your elbow against your side.