The roll:
You start out sitting on the floor, with your knees bent, feet hip width apart, about a foot or so infront of you, and your hands holding the front of your knees. You activate your core (with the breathing technique) and curl your tailbone towards the front, continuing until you've created a C shape with your torso and allowing your arms to straighten. Slowly, you pick your heels up off the floor, then your toes, so that you are balancing on the back of your pelvis, keeping your arms straight as you hold the fronts of your knees and maintaining the C shape. Then, you allow yourself to roll back, not far, just to the bottom of your shoulder blades, again maintaining the C shape, with arms straight, and using your breathing to bring you back into the balanced position.
I don't know if I've described it very well, but the balancing isn't the problem for us so much as the roll itself is.
So, there you are, the dreaded roll. Easy to do if you keep to the proper technique and once you have the knack of it, but hard on our already beleagured vertebrae according to my teacher.
Hugs,
Kat