Ultrasonic sensor

Hello guys I want to know that how an ultrasonic sensor works?
How we can make a distance measurer from it using uno?
Thank you

It sends out a loud, short shout of a typically 40kHz tone, and listens for the echo.
The time of flight is proportional to the distance travelled

Buy one of the ready-made units

Can you give me tips of making distance measurer. As I am beginner I don't know very much about it

Don't send more than about 20 pings per second, or you risk mistaking a late, distant echo from an earlier ping as a closer echo.

LMGTFY

Thanks everyone