As you begin to rise up after the pop, flick the board with the ball of your rear foot so that it flips to the side on the way up. Don't push down - that will send the board down. And don't push too hard away from you - that will send the board way off to the side. The trick is to figure out how to flip it under you. Catch this trick with both of your feet at the same time if possible.
Many people catch it with their front foot first, but two feet is always more solid.
This trick feels great when it smacks you hard in the feet. Once you get it figured out, you can learn to pop it higher by kicking it harder and extending your legs more when you flip it, but that comes later. Skateboarding is an inherently dangerous activity that can result in serious injury or death. We recommend that you seek proper training and equipment before attempting this activity. Inc. How things get done.