Question

mention one way in which we put echoes to use.

Answer 1

the use of echos we can see in sonar devices

Answer 2

When animals such as bats and dolphins use echoes, it is called echo location. They use it to find their way around or to locate prey. Echo location describes the way of how some animals detect the size and position of objects around them. At night, bats use echolocation to guide them in flight.

You can refer to this link :
www.tutorvista.com/content/science/science-i/sound/echoes.php