This may not be what you're looking for, but I learned most of what I know about matting and framing (and I do a lot of matting and framing as part of my photography business... The 'carpentry' as well as the 'artistic' parts) by attending a few classes at the art supply store in my town. I think I took 3 or 4 of them, and they may have cost me $20 each plus materials.

In my experience learning matting and framing on the internet is kinda like learning photography on the internet... You can get some of the theoretical stuff on 'teh interwebs' but unless you're actually out getting your hands dirty practicing the skills it's not going to mean much.

Having said all that, if you're looking for a 'one complete resource' for everything related to matting and framing (yes, the carpentry, but also a lot of detail on the art and theory behind how and why) then I'd recommend checking out 'The Complete Photo Guide to Framing and Displaying Artwork,' which, despite the rather unwieldy title, is one of the best references on the subject that I've come across.