I had the same issue when mine was new since there is nothing that says "screen on" and I was afraid to start pressing buttons randomly. Just press INFO to the right of the screen, then TRIP INFORMATION on the touch screen. It's the far left choice on the touch screen for me.
Yes, TRIP INFORMATION is the key. Was careening down the interstate at 75 mph a couple weeks ago and the co-pilot somehow got the display blank. It was driving me nuts! The trip information button was the key, but I couldn't figure that out until getting off the hiway. It should be more intuitive than that