How does the Audi A5's all-wheel drive system function?

I have been looking at the new Audi A5 and have heard that it has all-wheel drive. I am not familiar with this type of technology, can you explain how it works and the benefits it provides?

The Audi A5's all-wheel drive system, also known as Quattro, distributes power to all four wheels for increased traction and control in various road and weather conditions. This technology continuously monitors road conditions and can transfer up to 70% of the power to the rear wheels when needed.