The ab wheel is used to work the entire abdominal region by strengthening and stretching the muscles of your core.
Begin by gripping the ab wheel while kneeling on the ground. Your head should be over top of the ab wheel to start. Begin the exercise by slowly rolling the wheel straight forward. Go as far as you can and fully stretch out your body until it nearly touches the floor. Not everyone will be able to go that far, begin by going as far as you can and work your way out further as you get stronger. Pause slightly at the stretched out position and then pull the ab wheel back to the starting position; squeeze your abdominals to do this. Do not use your arms to move the wheel, keep them extended the entire time. Repeat this movement until you complete your set.
This movement should be done slowly and keep your abs contracted the entire time.
Once you have mastered this movement, you can also do this exercise by rolling the ab wheel to each side. Roll the ab wheel in a diagonal direction to each side of your body, this will focus on your obliques.
This exercise is not a good choice for someone with lower back problems.