Step 1: Cut a circle on one side of a box
Step 2: paint the box in the colours that you want. (this is optional)
Step 3: take rubber bands of different thickness and sizes
Step 4: arrange them over the cut circle as shown in the image. The tighter the rubber band, the better the sound.
Step 5: push a straw or pencil or any type of tube under the rubber bands to act as the "guitar bridge" as shown in the picture. And voila, you are ready to make some noise!