Need help on making a simple window for a building

I made a tower model and I want to make window textures to the faces i selected. I understand the UV mapping concept a little, but I’m having issues on trying to make multi- selected faces with a window image. Is there an easier method for this process instead of using UV mapping?

Probably would need to see at least a picture to determine if there is another way to do it. All depends on setup and that sorta thing. Typically on anything slightly complex, UV Unwrapping is the most reliable.

Here are some video tutorials that may help wrap your head around it (sorry, lame pun):
Introduction to UV Unwrapping
Unwrapping a Building

ok, i understand the uv concept, but what about texture paint? I tried to use it but when i save my blend file and re-open it, the texture paint work is gone. What am I doing wrong?