What does the Audi A1's efficiency program do?

I've heard about Audi's efficiency program but I'm not sure what it actually does. Can someone explain its role in the A1?

The Audi A1's efficiency program is a suite of features designed to improve fuel efficiency and reduce emissions. It includes technologies like start-stop system, regenerative braking, and energy recovery to optimize energy usage while driving.

Audi's efficiency program is also focused on lightweight construction techniques, such as using aluminum and high-strength steel in the A1's body, to reduce weight and improve fuel efficiency.