There are a large number of different ways to make rubber band guns. However, Instructables offers an easy method that only takes a few minutes. In order to make a rubber band gun, you will need two small rectangular pieces of wood, a hammer, a clothespin, nails, something sharp, glue and some rubber bands.
Nail the pieces of wood together
Hammer some nails into the two pieces of wood so that they are connected. You should attempt to make one of the pieces into a handle and the other the "barrel" of the gun.
Glue the clothespin to the gun
Take the glue and the clothepin and fix it to the back of the gun you have nailed together along the handle. This will make it so that you can stretch a rubber band across the top of the gun and squeeze on the clothespin to fire it.
Carve a notch into the front of the gun
Use the sharp object you have, like a knife or scissors, and carve a small notch into the front of the gun. This will create a nook that the front of the rubber band can rest in, and also make it easier for you to aim and fire your rubber band gun.