Imagine what happens when you drop a stone into a pool of water.
Waves ripple out from the spot where the stone entered the water.
Those water waves are similar to how sound waves travel through the air. When you speak or shout, your vocal chords vibrate. These vibrations go out in all directions through the air as waves. When the waves reach our ears, they make our eardrums vibrate too, so we can hear the words. But to get to our ears, sound waves need to travel through some stuff, like air, that can vibrate.