Oh boy, is this confusing.
I really appreciate the answers, which I've read over and over now, and I think I'm starting to get it. Sorry if I'm soaking this in at a Photography for Dummies pace, but could someone correct me if I have this wrong?
What I can do is put Tmax 3200 in my camera and set the camera to 400. (This is its fastest setting on the Canon 7s, and it has no exposure compensation controls.) Then, whatever my meter readings are for a particular shot, I stop down two stops. This is called rating the film or shooting at 1600.
When I'm done with the roll, I either process it at 1600 or 3200 (and at 1600 it may be easier to print, which is a big big plus). To get the time that I process it at, I find the chart for the film and developer I'm using, and go down to the ISO column to 1600.
Is that right? And this would be called pulling the film?
I looked up this up for Tmax 3200 and D-76, and it gives two options for 1600; why would I choose to develop it in stock or 1+1 solution, as the chart gives times for both? ((I'll be using D-76 for now, just because it's what I have bottles and bottles of in the house, but I'll keep in mind to experiment further with other developers.)