I just received rotator cuff surgery 6 days ago I have very little pain in my shoulder but extreme pain in my forearm. Y is that I had a patial teer and a full tear that was repaired along with spur and some burcitus that was removed I just donk know why

Referred pain. It could be referred pain from the shoulder to the forearm. Check with your surgeon. He/she may may have some home activities you can try to have it feel better.
That . That may be referred pain from the nerve. Keep an eye on it, and if it is worsen or persists, let your surgeon know, or if course if you had fever, increased swelling, or redness. Sometimes the surgery puts "traction" on nerves, and causes pain in odd areas after surgery.