This is how a Fuel Entry logbook page looks:
Instead of Miles and Gallons, it will show the units you have selected.
You tell C.A.R. if this was a fill-up or not. You can also ask C.A.R. to skip calculating MPG (or whatever you have selected for fuel economy) for this entry if you know it would be wrong -- you missed a fuel purchase, etc. Yes, C.A.R. will work with the real world.
If you click on the Calendar button next to any date on any page, a calendar will pop-up to help you pick a date: