I usually use bones from a roasted chicken and just throw them in a pot with enough water to cover them and simmer very gently for a few hours. You can add bay leaves as well but I don't add any other seasoning or vegetables until its almost done. The key is not to boil it and to leave it uncovered. It will reduce-that's fine. Once it is done (this really depends on what you like-a weak stock only takes an hour or two but a more concentrated one can go longer) you strain it and put it to cool uncovered in the fridge. Once it's cool there will be a layer of yellow fat on top which should easily be spooned off. Voilà. A concentrated stock can even be gelatinous. There are more complicated things you can do and steps to add but this is the basic method I use for soup and gravy.