Sounds are vibrations in the air that are caused by a vibrating object of some sort.
It is often not easy to see that the source of the sound is vibrating. Hold a piece of metal pipe and strike it with a wooden, rubber or plastic object. Try holding it and striking it in different places, until you find which combinations give the best sound. After striking it, gently touch the pipe in various places to see if you can feel it vibrating. Strike a tuning fork, bell or any metal object that continues to emit a tone for a time after being struck.