We are now calling them shaders.....
So start in TG Materials Library
https://planetside.co.uk/forums/index.php/board,56.0.htmlThere are many file shares here, tgc, that you may use on your models or examples of "how to" with image map shaders or image function
Hannes has a material file share here with examples of metals and glass , carpaint glossy etc.
WAS has added many good textures recently, also.
Depending on the effect you want, some use reflective or glass shaders coupled with a transform input (world) piped directly to the material input node.
Download a few shader clips and practice on a low poly model maybe; there are rules for textures but experimentation sometimes gives good results.
You will learn a lot from these texture combinations, merge options, transform possibilities, dissect them with trial and error.
Last option, share your model and see if anyone will show you what they know. I am currently trying to figure out a texture layering system for some spacecraft, sooner or later I will succeed. Life is fun!