While they are correct for the most part letme actually answer your question....
Provided that you have the trip computer (some A4's don't) the buttons on the windshield wiper stalk control it. There is a toggle like switch on the end and a RESET switch on the bottom. The toggle switch allows you to scroll through all the readouts the MPG one with the 0 with a slash through it is the average. Now in one of the top corners you will have a 1 or 2. The 1 gives you the readings from just that trip since you started the car after it sitting for longer then 20 minutes. The 2 means that it will keep measuring until you reset it manually by holding the reset button (handy for using it to measure MPG between fuel fillups) To cycle between 1 and 2 and additionally a mode that turns off the screen just click the reset button.

What about some specs and color combination info about your new purchase!? Pics?! haha