What are these things responsible for in the texture?

I don't know all of them but I'll try to explain as much as I can, someone with more experience may come here and correct me. I will explain these in the json format of materials because the cs is unsupported.

First normal vehicle materials:
"name": material name, CAN'T be the same as any other material name in the game or in any mod or else it will conflict, so make it unique
"mapTo": the material assigned in Blender (or any other modelling software) the game will assign your textures to.
"class": should be always "Material"
"persistentId": according to the devs this is not used anywhere so you can just copy it from whatever file and will work
"Stages": a table of 4 stages (not all need to have something in them). the first one is Stage 0 and it's special, it makes white things chrome in game. The others are Stage 1, Stage 2 and Stage 3. They work like layers, it will put the texture from Stage 3 on top of Stage 2, which will be on top of Stage 1, etc. Inside the stages are:

• "colorMap" - the colors of the texture. For Stage 1, and for everything you want to be fully white, use "vehicles/common/null.dds". For everything you want to be transparent (to show the layer below), use "vehicles/common/null3.dds".
• "diffuseColor": Alternative to above, you can specify a color using the R/255 G/255 B/255 A*2 format
• "normalMap" - google this to know what it does, it's complex. You have to use the same one on all stages. If you don't need to have it, use "vehicles/common/null_n.dds".
• "pixelSpecular": You should keep this as true because only old mods don't use it, not sure what it does.
• "specularMap": You have to google this one too, for stage 0 and everything where you don't want to have a specular map use "vehicles/common/null.dds".
• "specularPower": how strong is the specular map. Stage 0 should always have 128 on a vehicle, then all others progressively less, the best values to use are power of 2 but anything you can divide by 2 will work too.
• "reflectivityMap": A custom reflectivity map, you don't need to have it most of the time unless if normal reflections look bad
• "useAnisotropic": No idea but everything seems to have true here

"alphaRef": everything seems to have 0 here, idk what it does
"dynamicCubemap": it decides whether the part will use dynamic or static cubemap for reflections, you can always put true because it will look way better this way
"materialTag0", "materialTag1": Just tags the devs use to find materials easier, you can probably just copy them for whatever material. For tag 1 you can use "vehicle" or "object" depending what it is.
"translucent": Not sure what it does, but use false only if you have a reflectivity map
"translucentBlendOp": If you want the material to blend with others, you can use some options like "Mul", "Add", "Sub", etc. But 99.99% of the time you want to leave it as "None".

Now for skin materials:
You have to name your skin material like: "name of material you want to change.skin type.name of the skin", so for example "pickup.skin.parkranger", "hatch_seats.skin_interior.blue", etc. Do the same for "mapTo". You copy the rest from the normal materials for this part except you change something in the last stage:

• "instanceDiffuse": use True if you want to change the white on the colorMap to colorable with the 1st color in the palette.
• "overlayMap": the texture you want to use on your skin. It will use the 2nd UV map you have assigned in Blender (or any other 3D modelling software) by default.
• "diffuseMapUV": if true then it will use the first UV map instead.
• "colorPaletteMap": the color palette map your skin will use if it's colorable. Red means the part will use color 1, green color 2, blue color 3, transparent means none. You can mix these colors too. By default it will use the 1st UV map. If you want to make the whole thing colorable with 3rd color, use "vehicles/common/nullcolormask.dds", and with second use "vehicles/common/nullcolormaskG.dds".
• "colorPaletteMapUV": if true then it will use the second UV map instead.

You can also add another stage here (most vehicles use 3 by default so there is space) to add something non-reflective on top like dirt, rust, etc.

As for map materials, sorry I don't get them, but they are automated anyway. I hope I helped.