Napalm is a highly flamable liquid and when profesionally made it is capable of tempratures of up to 2,760 degrees Celsius (5,000 degrees Fahrenheit). The type I will show you how too make isn't that strong but it will be good enough for most ambitious pyros.
You will need:
* styrofoam (Lots)
* petrol
All you need to do is get a container and top it up with petrol (1/2 - 2/3 should be fine). Now, simply put the styrofoam into the gasoline. Watch as it completely dissolves. Continue this process until the mixture becomes a bit thicker. You may also want to leave it to set for a while after you are done adding how much you want.
You now have a crude form of Napalm!
OR
Do the same thing with pure soap instead of styrofoam. It has basically the same effect.