What does the Audi A2's automatic start-stop system do?

I've heard that the Audi A2 has an automatic start-stop system. What is the purpose of this system and how does it work?

The automatic start-stop system in the Audi A2 is designed to save fuel and reduce emissions by automatically shutting off the engine when the vehicle is stopped, such as at a red light or in heavy traffic. It works by using sensors to detect when the vehicle has come to a complete stop and then switches off the engine.