The hill-start assist function helps you drive off on a hill. 

If you hold down the foot brake for a time when the vehicle is stationary, the brake pressure is retained for brief a moment after you release the brake pedal – relaxed starting on any hill or incline with no roll-back. As you change from the brake to the accelerator, the car remains stationary for long enough and – thanks to the system’s automatic braking intervention – you can easily pull away without rolling back. Hill-start assist is a particularly valuable feature in combination with a towing bracket.

Article source: audi.co.uk