HOW: Get set up seated upright with your hands supported on your thighs. Begin the exercise by rounding your upper body and head/neck forward, letting your spine bend forward as your hands slide down your thighs. Reverse the motion to sit upright nice and tall and let your back/spine arch and extend. Repeat
FEEL: This should feel like a global stretch to your upper/lower and mid back depending how far you move. As you round, you should feel a stretch in your back, as you arch and squeeze your shoulder blades back, you may feel a stretch in your chest and shoulders. This should feel like a gentle motion that you're in control of.
COMPENSATION: Limit movement to your upper body, keep your lower body still.