How SONAR is made?

Depends on what type of sonar as in the technology used by navy to identify under sea contacts then:

A sonar is a method of detection most commonly used by the navy. It works by emitting a sound into the water of which goes down and when it hits something it bounces off that object and will return to the emitter of which is timing the time between the creation of the sound and the receiving of it. This time is the easiest way of identifying the depth of the object.

In there simplest form they are a speaker a microphone and a electronic timer oh and some water.

1) Release a sound into the water whilst starting the timer which is rigged to turn off when the microphone receives the sound.

2) wait for the sound to bounce off an object or the sound to hit the bottom of the object holding the water.

3) as soon as the microphone receives the sound the timer will shut down and you will know the distance of the object after you convert the time to distance.