What does the Audi A1's lane departure warning system do?

I'm considering buying an Audi A1, and one of the features listed is a lane departure warning system. Can someone explain what this system actually does and how it works?

The lane departure warning system in the Audi A1 is designed to alert you if you are veering out of your designated lane on the road. It uses sensors to detect the road markings and will give you a warning if you start to drift out of your lane without signaling.