Hi - what it sounds like - something pinching (impinging) on something else.
In your case, it sounds chronic, the bone has developed in your shoulder in response to the stress on the injury and it is rubbing therotator cuff.
As Physiobob has said, read the link provided...
As for the operation, the surgeon will remove the offending bone, sew up the holes etc. You will be looking at 3-6 months without normal use of your arm and getting to know your physio well!
Good luck