It’s always a good idea to ask any health care professional working with you to explain what you (or they) are doing and why. Having a good understanding of how your exercises work helps motivate patients to keep doing them and doing them correctly.
The scapula (your shoulder blade or wing bone) links the humerus (upper arm bone) to the trunk. Without it, you wouldn’t have normal shoulder movement. For every degree the scapula moves, the arm can elevate two degrees.
True shoulder motion is really a combination of scapulothoracic movement and glenohumeral motion. Scapulothoracic refers to the movement of the scapula against the trunk. The glenohumeral joint is what we normally think of as our shoulder joint where the round head of the humerus fits into the shoulder socket.
Many patients only work on glenohumeral motion without paying attention to scapulothoracic movement. It sounds like you are on the right track!