Rotation of spine.
Rest on your back. Hug your knees into your chest. Either cross one leg over the other, or keep your knees parallell. Allow your knees do drop to one side, and the opposite arm to the opposite side. Allow your neck to rest in comfortable position, either keeping your nose pointing against the ceiling, your knees or your opposite arm.
There´s not one way to do this pose. Feel the target area, and modify the pose until you feel the target area, and can allow your muscles to relax.
Stay around 2-5 minutes. Then slowly ease out of the pose and relax a moment before you shift leg.