Basically what Justin said.
As far as the Ranger is concerned, you either have single cab, supercab 2 door, or supercab 4 door. Which the 4 door is obviously the one that has the small rear extended cab doors which open up. The supercab 2 door is still an extended cab, but the rear small doors dont open but still gives you the look and room back there (if thats what you want to call it lol) but you just have to slide and tilt the front seats forward to get back there.
Supercab and supercrew are just terms that Ford uses for their trucks. For instance an F150 supercab will be an extended cab, and supercrew will be the model that has 4 full size doors.
Dodge calls their crew cab the "quadcab" instead of "supercrew" that Ford uses; again it just the ways each different manufacturer uses specific terms for their vehicles.