Can someone tell me how to make bows set things on fire? I tried enchanting, but it doesn't make them set things on fire.
You need a specific bow enchantment to set things on fire: The Flame enchantment.
The enchantment you get on an item is going to be randomly chosen, so you'll just have to keep trying until you get a bow that has one. It should be noted that the probability of getting the Flame enchantment on a bow is fairly low, and if the modified enchantment level is less than 19 it is impossible to get.
If you are in creative, you can look up the enchanted book with the Flame enchantment, and with a normal bow, combine them in an anvil, and you get the flaming bow...