>>322751191
easiest place to start is on vrcmods. find some okay model even if you don't quite like it and use it to learn the basic import and upload process. Second easiest is booth, buy (or download) some loli in a sailor outfit and use your new skills to get it in game. Third easiest is mmd models, which is a decent forcing function to learn very basic blender/cats as well as unity.

After you get the flow of just importing/uploading something premade you can learn to do basic edits to the textures and materials, shapekeys and animations in unity, then move over to blender and learn basic clothes swaps, then custom modeling, etc.