Its easy to do but hard to master...basically it involves twirling your legs around in the air (like a windmill) while your whole body rotates around so you can push your body to twist (when you legs are pointing down amd your stomach is pointing towards the ground, but support yourself like a cricket) You then push with your hands so your legs stay in the air, then when you legs are facing upwards, (you are on your back) you twsit your body so you can meet the floor with your hands, and support it again (like a cricket), then when your legs come around again, you are on your back again, and the process continues. in the top picture you can see the guys legs are twirling, and his hands are supporting his body, the guy in the bottom pic is about to lie on his back, his windmill is also better as his hands are very close to his chest. when you start out, you will probably find it easier to support you body with your arms underneath your stomach, as you practice and your method gets more advanced, you can even hold onto you balls while you spin, making a variation of the windmill, called the eggbeater.. really classy staff. The stretch windmill is reaching out with your hands so instead of you hands supporting you body, you abs are...but this takes seriously strong ab muscles.