If I read someone else's tutorial.. I'll just get confused

I just know how I do it... if my methods conflict, just ignore me..lol
The theory is pretty simple.. if the cropped and aligned
BITMAP is say 783 X 342.. the box needs to be 78.3 X 34.2 (or 7.83 X 3.42).. You get the idea.
If that's the case, simply appying it to the part makes it fit perfectly 8-) ... you might have to rotate it in the image software, etc.
You can use a UVW if you like just leave the 'Gizmo' alone.. adjust ony the axes of application.
Keep fiddling.. it will make sense. :)