Sound

Pressure waves in a material.

How it travels

Sound is a pressure wave and needs a medium, so it cannot cross a vacuum. It moves at about 343 metres per second in air and much faster in water and solids.

Counting seconds between lightning and thunder gives roughly a kilometre per three seconds.
Pitch is frequency and loudness relates to amplitude.

The Doppler effect

A source moving towards you bunches the waves, raising the pitch, and stretches them as it leaves. The same effect in light is how the expansion of the universe was discovered.