Sit on a chair, place your hands in front of you, palms up. Without moving your upper arm at all, rotate your arms out to the side. That's the easiest exercise I know for that. These are small muscles, you never use much weight. If you get to the point you want more, add reps.
Have your PT guy show you how to do vertical external rotation. It's easy to do it wrong, esp. at the beginning. It also often doesn't get covered in PT. The other one I do a lot is called Y. If any of these hurt, don't do them. You bring your hand up and across your body until it's straight up. Most of these can be rehabbed without surgery, but that's up to you and the Doc.
My typical PT schedule is every other day, lots and lots of reps, and more exercises than they ask for.
Once you get cleared for PT, hit Youtube for more pt exercises.
Best of luck.