Vibration is the source of all sound. Vibrating objects push against the air (or other medium- you can substitute water, jello, or whatever) around them, creating little zones of compressed air . The zone of compressed air pushes against the air around it, which pushes against the air around that, and so on. Between compression pulses the air "springs" out past the pressure where it began, creating a zone of less pressure, or rarefaction. You end up with zones of compression and rarefaction that travel outward from the sound source, one after another at a rate equal to the rate of that source's vibration. These, friends, are sound waves.