To perform the ab wheel roll-out, firmly grasp the ab wheel and kneel on the floor. Your toes and knees should be touching the ground. Then slowly roll the wheel while you stretch your body out. Keep your arms straight.
Once you are fully stretched out with your arms out in front of you, then wheel backwards and return to your starting position.
A key to this exercise to fully get the most out of it is to go slow. The slower you go especially when returning to the start position the greater the workout for your core (and also the burn!)