Step-by-step explanation:
RADAR is the radio, detection and ranging.
Suppose, you are using the torch to search the object in the dark. The light travels out from the torch and reflects off the object. It bounces back into your eye. Then, brain computes how far away the object is.
In the similar way, Radar works. Suppose, an airplane is flying at night through thick fog. In this case, the pilot is unable to see where he is going. He uses the radar. It sends the radio waves only a part of time. The rest time listens out for any reflection of any nearby objects.
If the reflection is detected then there will be something nearby the plane. It can use the time taken for reflection to figure out how far the object is.