What is the role of the start-stop system in the Audi A4?

I have heard about the start-stop system in the Audi A4, but I am not sure what it does. Can someone explain its purpose and how it works in the car?

The start-stop system is a feature in the Audi A4 that automatically turns off the engine when the car comes to a stop, such as at a red light or in heavy traffic. This helps save fuel and reduce emissions. It will start the engine back up when you release the brake. It's a great feature for city driving and can be disabled if desired.