What is sound and use how …

Sound is produced when something vibrates. The vibrating body causes the medium (water, air, etc.) around it to vibrate. Vibrations in air are called traveling longitudinal waves, which we can hear. Sound waves consist of areas of high and low pressure called compressions and rarefactions, respectively. 

There are two types of sound, Audible and Inaudible.

Inaudible sounds are sounds that the human ear cannot detect. The human ear hears frequencies between 20 Hz and 20 KHz.
Sounds that are below 20 Hz frequency are called Infrasonic Sounds. Elephants use Infrasonic sounds to communicate with herds 100s of kms away.
Sounds that are above 20 KHz frequency are called Ultrasonic Sounds. Dogs, Bats can hear high frequency sounds.