One of the most popular skateboarding tricks you will find is the casper. It's a fairly easy skate trick that plays off the kick flip but learning it can be a challenge, just as with any new trick. It's well worth it to put forth the effort because it leads into other tricks. The casper will help you learn technique and control so that you can better master the board for this and other tricks.
Here are the basics of how to do a casper:
Place your back foot on the skateboard tail. You will need your lead foot just over the edge of the skateboard's deck and just below the front trucks. You need your lead foot at an angle, mostly off the board. If it's too high or too low, you're going to fall.
Your back foot won't move because it kick flips the tail of the skateboard. Bend your knees and jump, making sure to kick flop the board and move your lead foot around in almost a U-turn motion. It will pull off the board and around to circulate.
This motion will make your lead foot comes down over the skateboard. Now put your front foot and back foot back on the skateboard. Land on the board, bend your knees and control the board with both of your feet. Now you have "stuck" the casper.
It sounds like a long description for what is actually a short move but it will probably take a lot of practice to get it all down to one fluid motion. If you try to do it too quickly, you will probably mess it up and if you try it too slowly, your board will just fall and not flip properly. It's important to get just the right speed and momentum going to get the board to move like you need it to. Once you master the casper, you are in a good position to start learning other tricks that build off of this one.
Video: Here's a cute video of a kid showing you how to do a casper . It's actually a really great video explanation and he shows you goofy and regular footed foot placements.