This is a very nicely done video tutorial by Robert Rodriguez on how to mat and frame a print (photographic or otherwise).
This is pretty much the exact process I use although I buy my mats pre-cut.
I realize that some who take photography seriously don’t make prints of their work but for me, making fine art prints and framing them seems to complete the process in a nice way. I like physical objects, not just a photograph on a web site.
I also print and assemble notecards and I think I’ll do a post on how I do that since I’ve made thousands of them and I’ve got that process worked out.