lots of computers, with radar, lidar, video and sonar sensors.
There are radar, lidar, video and sonar senders and receivers, with which the computers build up an image of the surroundings. That is combined with GPS location data, and input from the operator as to destination and route. Map data is stored internally which includes speed limits and info on lights and other restrictions.
Computers put this all together and send speed, braking and steering info to the car's controls. If all goes well, you get to your destination without problems.
Waves? that is what radar, lidar, video and sonar use.