Sounds are nothing more than disruptions in the air. They can happen with varying degrees of intensity (amplitude) and frequency (frequency). Amplitude correlates with loudness, and frequency correlates with pitch (how high or low the sounds are). Sound waves can also vary in complexity, giving rise to a given sound's timbre. Sound can be transmitted by materials other than air.
Sounds are produced when objects vibrate. As they vibrate, particles of air are pushed together in a particular pattern. this pattern is a sound wave. Sound energy travels in compressional waves. In this, matter vibrates in the same direction as the energy travels through it.