All the different versions of FulGaz display the same data on the ride screen, but the iPad displays all the information at the bottom of the screen. Simply put the large numbers tell you what is going on right now, the smaller numbers provide extra information.
Most of the information will be familiar in one way or another from your bike computer or other apps. The exception to this is the small number above the "Current Speed" reading. This is your speed relative to the person who filmed the ride. If it's usually below 1.00, you're going slower than the person who filmed the ride.
Don't get stressed or overly focussed on this number, the people who film the ride range from Olympians to retirees, so you can't use it as a universal form guide or someone to ride against (we created Challenge mode for that). It is handy as a guide to know how long the ride will take you to complete.