G Vivanco,

This is a really deep area, but the basic answers to your questions are:

Linear vs Gamma-Corrected: Linear is an even adjustment of the curve, black to white, whereas Gamma-Corrected is logarithmic and will put more emphasis on the shadows. The first is the default but I prefer working in the second. In theory, the second works more like your eye sees the world.

RGB vs Luminance is easier. RGB adjustments will affect the color (tint) of your image and Luminance will only affect exposure. Same goes for the auto-buttons. If you just want to fix exposure, use the Luma (Auto-black/white icon), but if there’s color correction needed, try the RGB (Auto-color icon). Often you just have to try each and see which you like better.