If you are writing a novel with a real world setting, you probably use some kind of map as a reference in order to make your world as real as possible, and to keep your characters from accidentally making a wrong turn.
When you are creating your own world, it's no different. You need a map. Chances are, you already have a map of your little world in your head. But it will be very easy for your characters to get "lost" or accidentally head east instead of west if you don't have a map to refer to. So, I suggest drawing one.
You don't have to be an artist in order to do this, because this is primarily a reference tool for you to use as you're writing. Here are some links to help get you started:
Have fun mapping!