Stir fry is one of the easiest and most flexible foods to make. It's really hard to ruin; you just put in random amounts of various vegetables, add a protein of some sort if desired (meat, cooked or canned beans, or chickpeas work well), fry a bit, and serve.
Or, you can take the same mixture of vegetables and throw them in a steamer for 5 or 10 minutes. Steaming gives a different flavor and texture, but is also good.
I don't own a wok, so I just use a frying pan for my stir-fry.
If I'm using meat in the stir-fry I like to toast my garlic and onion in a bit of oil the pan first so the meat picks up some of the flavor. Then I remove the garlic and onion to another dish and fry the meat, adding the garlic and onion back in with the other veggies. You can leave out the onion, garlic and oil if you need or want to; they're not really necessary at all.
Incidentally, if you use much garlic a decent garlic press is definitely worth the $5 or $10 investment. I use mine all the time. It's so much faster than mincing garlic with a knife. The trick is to rinse the mashed garlic out of the press before you put it in the dishwasher, or it will be hard to get clean.
While the meat is cooking I wash and cut up vegetables, stirring the meat frequently. I do the firmest vegetables first, because they take longest to cook.
When the meat is almost or barely done cooking, I start adding vegetables as I cut them up. I'll put in hard things like carrots, potatoes, turnips and parsnips first if I've cut them into chunks or slices. If they're grated, you can add them at the same time as the softer vegetables and they will cook faster.
In general, I add the hardest vegetables first and the most delicate vegetables last. Something like lettuce, corn or peas takes very little time to cook, so it will go in just before serving. You can throw in any leftover cooked vegetables at this time, too, and just heat them before serving.
If you are using tofu or cooked legumes, you'll want to add them with the soft vegetables or at the end of cooking so they don't get overcooked and broken up.
Kale, although it is a leafy vegetable, takes longer to cook so you'll want to add it earlier. I usually blanch broccoli for 1-2 minutes in boiling water before adding it to a stir-fry; it has a better color and texture that way, and cooks faster.
I often cover my stir-fry with a lid or some aluminum foil to help hold in the heat so it cooks more quickly and evenly. Stir frequently so the veggies don't burn. Cook just until the veggies are starting to get tender and brown a bit on the edges.
Most vegetables have quite a lot of flavor, so extra seasonings really aren't necessary, although you can add them if you like. I usually use just salt, maybe a dash of pepper, and sometimes some sesame oil.
Last night I made a stir-fry with a minced clove of garlic, about half a leek, a pound of ground veal, 4 or 5 smallish carrots, 3 stalks of celery, 4 leaves of kale, and a zucchini, all sliced thin and added in that order. It was delicious.
Other vegetables that are good in a stir-fry include turnip, jicama, parsely, cabbage, bok choy, mushrooms, corn, tomatoes, cooked beet, green beans, yellow squash, peppers, eggplant, cauliflower, cooked cassava/yuca, bean sprouts, lettuce or just about any vegetable you enjoy and can tolerate. Some fruits such as apples or citrus fruits add a really nice touch to a stir-fry, too.
You can serve a stir-fry over some kind of a starch or grain (noodles, spaghetti squash, rice, cubed bread, any cooked grain, or a mashed root vegetable such as potato) if you want to. Or, as we did last night, you can simply eat the stir-fry by itself.
It's a great thing for someone who doesn't cook much to try making, because it's such a simple and flexible dish.
A basic rule of thumb if you're making a stir-fry for the first time might be to choose 5 ingredients or fewer in addition to your protein and seasonings. Don't make it too complicated for yourself at first. If you add too many different things and cook it to long, you can end up muddying the flavors. It will probably still be good, but keeping things simple seems to make it even better.