Originally invented in 1987, the "Superman" has the rider taking both feet off the pedals and stretching their body to the back to look like Superman flying. It has a few variations like the "Superman-seat-grab" (where the rider grabs the seat instead of the handlebars), or even the "Superman-nothing" (where the rider stretches and lets go of the handlebars for a moment, flying completely off the bike!).
You should do this on a jump that will give you a decent amount of hang time, especially when you're first learning it. A tabletop with about a 10-foot gap should be good. Once you have Supermans dialed, you can do them faster on longer jumps.
Be sure to slide your feet off the pedals gently. If you push off of them, you'll push the bike away and you'll probably wreck.
When you push the bike in front of you, do it gently, with the momentum from the jump. If you push too hard or jerky, you'll lose it.
As you get more comfortable with the trick, you'll be able to stretch out more.
BMX freestyle 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.
Always wear a helmet.