Did you know that your a sound source and reciever. Yeah you can hear and translate sound and then make sound.
Where the first arrow is, that's your ear drum which when a vibration hits it, it triggers the hammer, anvil, and stirrup other known as the ossicles which send the vibrations through the cochlea to the brain.
Pitch changes when the object making the vibrations (sound) is shorter or longer. If its longer then it's a low pitched sound or vise versa it's shorter and it's a higher pitch. An experiment is to lay a ruler and have some of it hanging off and and push it down and then release it then change how much is hanging off.
In order for sound to travel it needs a medium such as air, liquid or a solid.