Answer:
The vibrating sound source moves in such a way that the air around it is also made to move. Imagine a drum skin being hit hard with a beater. The skin moves to one side and squashes or compresses the air next to it. This compressed air "pocket" in turn pushes and compresses the air next to it while the "pocket" itself bounces back towards the position it came from. The compressing effect and stretching effect therefore moves outwards from the sound source. The movement of the air back and forth is itself a rapid vibration and the movement of the effect outwards is in a wave form. Eventually the effect reaches the ear and is made into signals which are sent to the brain.
