Looking for a tutorial/wiki on materials, textures and decals

Most of the tutorials I’ve found haven’t really helped me in creating my own textures. I can create an image that looks like concrete but then I never know how to save it as a texture or apply it to a mesh so that it doesn’t look weird.
I tried to import a texture into 3DSMax (trial version) and it never works.
I get to a certain point and what they show in the tutorial isn’t what I see in my program, (3DSMax, Blender, Photoshop Elements, Gimp). I need something that explains it in beginner terms.

I see other stuff (uv wrap and “normal”?). I also don’t know what they are for. Is it so the 2d image will fit on a 3D mesh? How do you make sure the texture isn’t too big or too small? Do you know what size texture you will need based on the size of the mesh or do you make the texture a certain size and make it fit the mesh?

Google for “Unreal Decal”, follow the link to the Unreal documentation, or check out YouTube…