Hang from a vertical object with a wide grip and bring your bent legs up, so that your upper body is vertical and inverted and your legs are tucked.
Pull with the top arm push with the bottom arm.
You can get into the position by hooking your feet on the support and walking them up until you are inverted, but if you do that be careful that you have enough strength to go back down.
Risks
You will be inverted and at some distance from the ground; make sure you can safely go back down before attempting.