If you want to add artwork then you would, typically, not use a fabric.
The following link, provided in this forum, has link to documents including one about fabrics...
https://forum.reallusion.com/251007/Training-%E2%80%93-Tutorials-Guides-and-Online-HelpIn this document, the layers are broken down into:
Maps, Fabrics (up to 7 different ones), Decal, Pattern and Effect.
I am guessing that the proper place to put your artwork would either be the Decal layer or the Pattern layer (depending if it is a single piece of artwork somewhere on the clothing or a pattern artwork covering the entire clothing). The Fabric layers are typically used to determine which part of the clothing uses what fabric. The Fabric document shows a pair of jeans with a belt as an example. The jeans are made from one material, the belt from a second and the belt buckle from a third. So fabric one may be denim, fabric two might be leather and fabric 3 might be metal. The Decal and Pattern layer, as I understand it, is used to add things "on top" of the material. As I understand it Decal is used for a single (non repeating) addition because you specify in the map the exact location of the decal. Pattern, I am guessing, is more of a fabric type entry where the pattern is applied to the whole of the fabric.
The document is only 15 pages and most of that is screen captures so I'd recommend looking at it. It does not answer all the questions but it will probably provide enough information to get do what you need.
"We often compare ourselves to the U.S. and often they come out the best, but they only have the right to bear arms while we have the right to bare breasts"
Bowser and Blue, Busting The Breast