Heat a can of beans (pinto, kidney, black) - optional: heat a little oil in the pan first and add a couple of tablespoons of chopped onion and a chopped garlic clove. You can also add a dash of cumin/chili powder/cayenne.
Heat tortillas on a dry pan (pref. iron - I think this gets too hot for nonstick) or in the oven.
Serve with chopped lettuce, tomato, shredded cheese, leftover rice, sour cream, salsa, whatever you like.
We have this at least once a week!
PS There is a book, I think the title is "Cooking Without A Cookbook" which is very good and basic. What we also do when learning a new cuisine, say Chinese, is get a cookbook and make several dishes exactly according to the recipe. Learn the technique and the spices that way, and then go off on your own (substitutions, etc.)