Sound travels through the air in the form of vibrations. These vibrations cause particles of air to compress together and this causes the air around them to move in such a way that they are driven in waves away from the source.
The way that sound travels is an oft discussed topic in basic science for younger children. Many kids can easily identify a source of sound and understand how the ear detects it, but struggle to understand the process in between.
Just like light, sound travels in waves caused by air molecules that vibrate. If a drum is banged the air molecules around the drum vibrate, and these vibrations cause air molecules slightly further away to shake in turn. The process repeats until the vibrations lessen and the sounds begin to dissipate.
A simple toy slinky is an excellent tool for demonstrating how sound waves work to budding scientists. Stretching a slinky across a desk and pushing one end rapidly illustrates the compression that causes air particles to bunch together as the wave is sent along the spring. The parts of the spring representing air molecules do not move and simply vibrate, while the wave noticeably bounces back towards the end that was pushed, representing an echo.