It can not be clear yet, but before you can use your "pre built" textures you need to pass by the process to unwrap your model which at the end you will get an image "blabla_auv" - the texture created by wings - exactly as you saw in those videos. This texture can be exported (made external) and can be edited (painted) or replaced by your own image. (I think I made a video showing that too)
Texture images must have a power of two size. Usually 512x512, 1024x1024,...
Texture images must have a power of two size. Usually 512x512, 1024x1024,...