Commonly people like to explain how the ear works. Here we like to concentrate less on the physical part and more on the physiology, explaining the hearing process.
Humans are born with ability to hear sounds (actually we can already perceive sounds before we are born) but the ability to derive meaning and information of the sounds we hear is a learned/acquired ability.
This ability develops along with our general brain development and the development of our other senses, especially sight. From the moment we are born we feed our brain with auditory information building up a memory of meaningful sounds which helps us to perform the miracle of hearing.
We reach our peak in our ability to hear and analyse sounds in our early twenties. From then on, in most cases, our auditory abilities gradually decrease peripheral as well as central and in combination.
How We Hear
If we just think about processing of sounds. Humans are able to process a vast range of different frequencies as well as intensities.
We can process frequencies from 20 Hz which is a very low, deep tone to 20,000 Hz which is very shrill and thin, with the ability to discriminative about 3,500 individual pitches.
Equally humans ability to process loudness is vast, ranging from extremely soft sounds below 0 dB to around 120 dB which is extremely loud and causes us to perceive pain, in about 1 dB steps.