the incomplete tear is bundles of fibers shredded beyond use. As long as the tissues are connected along the bundle, they will heal.
as stated complete tears will require surgery to reattach. Rehab is going to take 8 to 12 weeks for soft tissue to heal enough for you to start any rebuilding operational strength.
The attached muscle can be exercised but lightly and let pain be your guide . Pain means the injured material is being reinjured...Stop.
Maintain your range of motion in the shoulder but don't stretch when the injured tissue issues a pain warning.
There iis a method of rehabing using very low weight but with very high repetitions. this can be done after soft tissue phase of healing. If you rush the process you can reinjure the muscle, keep it inflamed, build greater scar tissue in the muscle.
I recommend a good Physical Therapist before an Orthopedic visit. A good PT can diagnose your condition and treat in many states without a doctors referral. Many states have what is called "Direct Access". A good PT will refer you to a Physician if it needs surgery. Good Luck on your recovery. Don't be a muscle head, go slow and read your pain.. Blitz