Your toes should be pointing upwards, towards the top of the water. Your knees should be at 90 degree angles. Your hips need to be at about 110 degrees. When your feet are flat against the wall, use them to push off. Your body should shoot off the wall like a torpedo. The harder you push off, the faster you will spring off the wall. As you are pushing off the wall, start rotating so that your back is facing the ceiling. Your belly will be facing down at the pool floor. Twist your hands and look towards the direction you want to twist. Don't move your head. After kicking off and during rotation, you can perform a few strong dolphin kicks. This is optional, and may be something you want to do after you get better. Swim around 10 to 15 feet ( approximately 5 meters) underwater using the butterfly kick in streamline position. Start the pull with the arm that was closest to the bottom as you rotated. Your hand should exit the water as you finish the pull. Now resume your freestyle stroke.

Summary:
Untuck your legs and press your feet flat on the wall. Straighten your legs as your push yourself off the wall. Rotate onto your stomach. Resurface and begin swimming normally.