If you are new to Pilates, this practical tutorial will introduce you to your 2 Girdles. Your Shoulder Girdle and Pelvic Girdle.
If you consider the role of a "girdle", it is to hold things in place... that is, provide stability and control. When we have stability, movements in the shoulder and hip can be done safely and with control. Movement without control is dangerous. That's when you do a movement and feel it as strain in your back, neck or shoulder for example.
When you do the same movement from a place of stability first, the movement doesn't hurt. If feels strong and fluid.
Check out this video (and do it with me as that's the whole point :) ... that you learn how to move better) and then you can do the Quickie 360 Core.