For your windshield wipers you're going to bring your chest up so that it engages your upper abs while also engaging your lower abs and obliques. Your arms are going to come into a T-shape with your body in order to keep stability for your lower back and you're going to go ahead and bring your legs up with a slight bend in your knees.
This exercise will greatly work your obliques. Simply tilt your legs to the right or left until you either touch the ground or get as close as you feel comfortable to the ground. Then, repeat on the other side..
This movement will resemble the windshield wipers on a car. Enjoy!