This is one of those pyrotechnic campfire amusements. It's really simple and pretty cheap.
You just take a metal bucket full of wax, a bucket just big enough for a large 3-wick candle is perfect, and boil the wax over a campfire.
Once the wax is at a good boil, it may start to burn, take about half a dixie cup (or about 2/3 cup if you want to be specific) and dumb it directly on the boiling wax, the more forcefully the bigger the result.
Be extremely careful if you're the guy with the cup as a large fireball can be produced. Be espically carefull if there is any wind, a slight breeze can make a dramatic diference, the fireball can reach over 50 feet tall so if there is any wind take that into account to ensure you do not put people or property in harms way.
Step 1: Don't Harm Yourself or Kill Your Firends!
THIS IS DANGEROUS.
I mean, seriously, how much fun would it be if it wasn't?
Here's a link to a video, it was taken at another time and you'll see the effects of a light breeze, mainly it's not as tall and flares out more.
I found this video of some stupid kids trying this, and this is what happens when you just pour a large quantity of water on boiling wax. It's called third degree burns.