There is a variety of different ways they do it. There are some places—I believe it's Norway, and I should have had this nailed down—where they have a standard across all fields as a function of your level. You come in as a master's student or in first year of your Ph.D, and you get a standard stipend. It builds up as you move through the program, just like it would in any other field where you gain expertise and your work becomes more valuable as you get trained. That kind of approach is very common.
Of course, in places like the United States, some institutions have very deep pockets, so they also provide funds out of, let's say, donations from alumni, etc., that can supplement these kinds of sources.
Then there are TAships, teaching assistantships. In our system, that happens as well. In other jurisdictions, there's a limit on how much TAship you do, whereas, in Canada, quite often people make up the difference of not having to go to a food bank by doing many, many hours of TAships, which means less time for their research.