There are no particular methods by which you can generate a musical tone from an instrument and it depends on the particular instrument that you are using to generate the tone. If we take the example of a percussion instrument, usually it generates a sound only when somebody hits the upper part with a special kind of stick or sometimes with his hands also. The upper part is covered with the skin which is usually made with the animal skin. The skin is tightly covered on the hollow part of the instrument. When the player hits the instrument a lot of vibration happens inside the hollow part and they try to come out of it but they are unable to do. It is for this reason that it produces the sound that every one loves.