>>74604805I mainly learned through trial and error, but you could use this video:
https://www.youtube.com/watch?v=vwRkPZVNSscHere's a quick rundown though: The Overlay Textures in CharaStudio will be layered on top of the main textures (usually used for extra body shading). The "MainTex" option in the Material Editor listing is the main texture and is the texture you usually edit and replace for custom accessories/bodytan shapes.
You might not need this for bodies, but I like to use a reference texture in-game and as a layer in my editor to check how the texture aligns with the model (since I'm terrible at visualizing otherwise). This is the one I use, but you can find other patterns by searching for "uv checker textures".
https://files.catbox.moe/amk1g3.pngAs a heads-up, I found the neck area (where the head and body textures meet) to be an absolute bitch to get the colors right when I attempted this Matsuri custom, more on-model tan... you can kinda see the line if you look close enough.
