I started by making the sauce (recipe here). It's very easy--basically just tomato paste with seasonings. This sauce has a little heat, but it gets diluted enough once in the enchiladas that it doesn't bother sensitive people like me.
Once the sauce is done, you assemble the enchiladas in a baking dish. I used brown rice, black beans, cheese, and of course the sauce.
When you've filled the tortilla, fold over the sides and flip it over--it should stay closed that way. Then spread some more enchilada sauce on top and sprinkle with more cheese. Bake them at 350 for 20-30 minutes, basically until the cheese is melted and the tortillas get a little crispy on the edges. (I've seen some recipes tell you to add more sauce halfway through, and you can do that if you like your enchiladas extra saucy.)