The basic concept of UV mapping is this: textures are flat, but your object is in 3 dimensions, so you need to unwrap and ‘flatten’ the model to tell the computer how it can apply the flat texture to your 3D object. The goal is to ‘unwrap’ your model without stretching any part of it too badly. It’s like wrapping a present but in reverse ^.^
The important thing to understand here is that once you’ve done the work of UV mapping you can apply ANY texture to it and it should work correctly. UV unwrapping doesn’t involve applying a material to your object, it’s just the ‘map’ that gets used when you DO add a texture.