I used to think, for some reason, that stir-fry was an elaborate meal that took a lot of time and planning. It could be, if you're using meat, but even then it's not really all that involved. One of my roommates once taught me how to make stir-fry vegetables, so that's what I'll be concentrating on here.
First step: rice. Rice typically takes 20-30 minutes to cook (or longer, if you're making a lot), So keep that in mind when you're timing your meal. If you're quick at chopping vegetables, or have them chopped already, or if you're using frozen, start the rice first and wait ten minutes or so before you start cooking the vegetables. If you're slower at chopping (like I am), you might want to chop your vegetables before you start the rice. You'll figure out the timing after you've made it a few times. I like to make at least one extra serving of rice so that I can have rice-in-milk for dessert or for breakfast the next day (that's a subject for another post, though). My point is that rice takes awhile to cook, so if you're making it anyway, you might as well make enough to use for other things while you're at it. But if you do make extra, make sure you know what you're going to use it for or it might just end up rotting in your fridge.
But back to stir-fry.
There isn't a set amount of vegetables or even a specified type of vegetables to use. Just make a guess at how much you'd be able to eat. If there turns out to be extra, you can have it for lunch the next day or freeze the extra serving(s). Veggies I commonly stir-fry include carrots, broccoli, cabbage, spinach, squash/zucchini, eggplant, and sometimes cauliflower. If you like peppers, onions, and so forth, you can include those. You can have any combination you want.
The frying pan I use does not require oil, but most pans do. You can also use a wok or a skillet - whatever you have handy. Start with 1 or 2 tablespoons of oil (I recommend olive oil or something similar that actually has flavor), heat it for a couple of minutes, and then add some garlic. Unless you don't like garlic. Then don't add it. But I love garlic, so like to add lots. I usually just get a regular spoon (like for cereal) and dollop some in. Start with 1 or 2 tsp if you're not sure. Once the garlic starts to cook, dump in your vegetables. If you have a lot, make sure you leave enough room in the pan to be able to stir. If you have veggies left over, store them in water in a covered container and use them within the next couple of days - you can make another batch of stir-fry or another recipe. And, like I said, stir-fry does freeze well.
Anyway. Stir the vegetables to coat them in oil, and cook until they're, well, cooked. It all depends on how you like them. Some people like it crispy, others like it more well-done. Just make sure that they're warmed through and not still crunchy. I've never actually timed it, but I would guess that it's probably 5 to 10 minutes of cooking.
Once the vegetables are at the desired state, add some sauce. I typically just sprinkle some across the top of the vegetables and then stir it in. Keep cooking long enough for the sauce to get warm, too. Remember that it's easier to add sauce than to take it away, so start with less and add a little until you have the amount that you want. The sauce you use is up to you. Some people just use soy sauce. I have used Worcestershire sauce. It's not my favorite nor the first thing I would recommend, but it wasn't horrible. Orange sauce is good. Some people use oyster sauce or peanut sauce. I recently discovered something called Gochujang - it's a Korean sweet & spicy sauce. One of the primary ingredients is red pepper powder, so it does have a kick, but it's mild enough that even this non-spicy girl can handle it. In moderation. The slogan on the brand that I got says "Goes with Everything" sauce. I have found with to be (within reason) true! I once put some on a spinach spanakopita, and it was really good! But I'm getting off topic again.
Actually, that's basically the end. Yep. Not much else to say about it. It is a super easy meal that has lots of potential for variation. And it's a great value - it gives you a lot of food for how much money you spend. One of my favorite things to say about stir fry is that you start with a big plate of food, eat twenty bites, and then you still have a big plate of food. It can go a long way.