I'm still getting my head around a lot of this stuff, but relative to the equator an inclination of 0 would be an orbit exactly along the equator prograde, 90 would be a polar orbit straight up from South pole to North pole, 180 would be exactly along the equator but now going retrograde. So if you split the directions on a circle representing an eastward rotating planet viewed from the side, using "clock face" terminology:
Equator runs from 9:00 to 3:00. 3:00 is 0 degrees (prograde equatorial orbit), sweeping counterclockwise 12:00 is 90 degrees. So orbits between 0 and 90 degrees are prograde, although I guess 90 would really be perpendicular). Continuing the counterclockwise sweep from 12:00 / 90, 9:00 would be 180 degrees - retrograde equatorial. Past that "upper half" of the "clock face" inclination range I find it a bit confusing as I guess you start counting is as -179 to -90 (6:00) and back towards 0. I'm not entirely sure of that as I don't think I've seen an orbit displayed that way yet in my limited time in Orbiter. Take these other guys word for it, they are far more experienced than I but I hope I at least got this right.
One more thing that really confused me at first: the prograde autopilot seems to always orient the planet to the left of the screen relative the the "upright" viewpoint of the spacecraft. Keep in mind that "prograde" in this case means relative to your orbital plane, NOT whether it's prograde or retrograde relative to the planet. So when you're orbiting the Earth and hit prograde, the surface is to your left and all the continents are upright like you would see them on a typical map. The standard Orbit MFD also always shows your graphical orbit of a planet in a counterclockwise direction, regardless of whether you're orbiting prograde or retrograde. So you have to pay attention to the Inc value. If it's in the retrograde range, you have to imagine that you're looking at the visual orbit plot from underneath the planet rather than above it. If you make a moon flight for example and enter into a retrograde orbit, and engage the prograde autopilot, it will again orient the surface to the left of your viewpoint. Except that in this case South is UP and you are actually flying upside down along your orbital path. It's all just a matter of perspective but I personally found this very disorienting at first, my brain just wants to see the planet in a conventional North is up, South is down frame of reference. So if I'm in a retrograde orbit and use the autopilot to orient prograde, I then usually bank 180 degrees to put the planet on my right so my visual reference is "correct". At least in a retrograde orbit the Map MFD will scroll right to left, which helps to get your bearings.
