Facing away from the sled, grab the straps so they go over the top of your arms. (This will be a stronger grab, and more comfortable than letting the straps go under your arms.)
Move away from the sled until the straps get tight and your hands are positioned near the lower portion of your chest.
Plant your feet into the ground as you press the straps away from you.
The straps give you the freedom to press at many different angles. The staggered foot stance is best. You'll be able to apply much more force into the ground. If you stagger, make sure to alternate your back leg with each rep. The back leg is the leg that drives into the ground and produces the force that will travel through the body and into the arms to complete the pressing motion.