Do you have a slow cooker? It makes life a lot easier. Portions are hard to say; if I've done a chunky soup I'll eat less than a thinner soup. Gradually I learn how many ladles makes "a bowlful" then I can do a big batch and freeze in knotted plastic foodbags.
Stock essentially is boiling up bones with some flavourings.
So for a chicken carcass I break it up a bit, shove it in the pot, halve a small onion (only peel off the papery skin), add a bay leaf, and a splash of white wine vinegar/cider vinegar. Pour over enough boiling water to cover the bones, put lid on, give it 2-4 hours (I don't like over-cooking chicken stock). It's ready when it smells yummy!
Vegetable stock - anything goes EXCEPT brassicas/crucifers (cabbage, broccoli, cauliflower etc). If you use a certain brand of stock cube, see which veggies they use. I'd start with carrot, onion, celery, bay leaf, leek? See how it goes.