I heard about them first several years ago at a university course where one student presented them in class. He showed some very interesting videos that I was just recently reminded of in a discussion regarding "life, the universe and everything" as Douglas Adams put it so nicely :-)
The inner functionality of these vehicles is quite simple. There is a light sensor that is linked to a motor. One example of a connection between these two could be: If more light is detected the motor will go faster, if less light is detected the motor will go slower.
If placed in an environment with light these vehicles exhibit very complex behaviour which we would interpret as love, fear, curiosity and various other emotional expressions. Braitenberg wanted to say how difficult it is to know about the internal structure and "thinking" of something when we can only observe how it acts and reacts.
There's a less fancy video, but showing the simplicity of the vehicle and it's reaction here:
A more fancy video is that of a spider