Sound waves are movements, or vibrations, in the air made by sounds. When these sound waves enter the canal of your outer ear, they hit your ear N drum, a thin, tough sheet of tissue stretched tightly along the canal that separates your outer ear from your middle ear.
As the sound waves hit, the ear drum begins to vibrate, much the same way that a drum does when it is hit with a stick. This vibration of the ear drum causes three tiny bones in your middle ear to vibrate too. They, in turn, send vibrations to a liquid that fills the deepest part of your inner ear. The moving liquid presses on the nerve cells which control your hearing, and these, in turn, pass the sound message on to your brain.
Some people can train themselves to shut out certain sounds while listening to others, as an orchestra leader does when he listens to each separate instrument even though many are playing together!