Making stock is stupidly easy, too. I was going to say that GF taught me how to do it, but actually, I think it was my mother. Mom's a very "throw stuff together and hope it works" sort of cook, but she's good at it. "Mix and match" suppers and "The Great Fry-up" are specialties of hers. She also makes a damn good turkey soup. She once showed me how to make that soup, but never told me how to make the broth. I must have gleaned the technique from watching her every Christmas day.
It's like the music thing. I don't know how I know it. I just do.
Start by saving the crap everyone else tells you to throw out (unless it's fuzzy or blue or smells bad). Those almost-slimy lettuce pieces from a salad. Onion skins that aren't quite brown. Celery leaves or asparagus bottoms or the tiny roots on beet greens. If you roast a chicken or have another sort of meat product with bones, keep everything you don't eat, including the cartilage or leftover meat. You can mix the veggies and meat or keep them separate. I generally keep mine apart (in case of vegetarian guests), but I recently made a ham and pea soup with a bunch of veggies and half an apple-roasted ham as the base (plus ham I'd scavenged from the dinner table of a family get-together).
Depending on what you're boiling, this step could take one to five hours. Bigger animals = more time (a good analogy for digestion, by the way). Give beef bones four to five hours, pork three to four, poultry one to two, and vegetables one to two, depending on how potent you want your stock. Once your water's turned a rich colour (anywhere from gold to brown to red, if you used beets), strain your stock through a colander - or just tilt the pot while holding the lid at an angle - into another pot. TA DAA. The pretty leftover liquid is stock! You can use it right away or freeze it or... drink it, I guess.
On an ending note, for all you folks who fit the "I'm too busy" category, remember:
1) Homemade stock is free, especially if all your scraps are scavenged instead of bought.
2) Homemade stock isn't loaded with salt (unless you dump it in there) and contains lots of vitamins and minerals that the process of preserving canned stock kills off.
3) You don't have to make stock right away (although you can; Mom always started making turkey stock as soon as the bird had cooled and been picked over). Even freezer-burnt meats and vegetables make tasty stock, so you don't have to stuff soup prep into an already busy day. Wait for a lazy Sunday.
4) An excellent tip from Mom: If you're making an animal-based soup, don't put the meat in with the stock bones. Add the meat last (because it's pre-cooked anyway) during your soup construction to keep it flavorful!