How stealth aircraft hide them from opponent?

A radar system sends out a wave. When part of this wave hits something, it bounces back to the radar receiver, the radar can then work out the size, location, and also the velocity of the object.

A stealth plane is specially made to scatter radar waves across its angular surface. The radar might not be able to detect it, or estimate that the object is far smaller than any military vehicle and therefore not sound any kind of alarm.