Physical therapists (PTs) are experts in movement and function, which sounds like a pretty broad topic to be an expert in, and it is. After physical therapists graduate PT school (now-a-days at the doctoral level), they find their niche and specialize. You can find PTs working with high-level athletes, children, infants, people who are recovering from injuries, people with neurological conditions and many other types of clients.
One of the great benefits to skin rolling is it increases the circulation in the area to which it was applied. Often times, areas that are tight or restricted are receiving reduced blood flow and oxygen. By bringing blood flow to the area, toxins can be cleared and the healing contents of the blood are brought to the injured area. Skin rolling can also restore the mobility of surrounding joints and nerves, which can help to restore normal function. By allowing the skin to move more freely, pelvic congestion, heaviness and aching can be effectively treated.
If you still do not feel these movements, you can try stopping the flow of urine when you are urinating. Feel the work that goes into that action, lifting muscles near your bladder, and try to mimic this movement when you do the exercises above. This is only recommended to try once as you are learning about the muscles. Do not repeat this as an exercise, or it can actually cause urinary problems.