You have a choice here. You can use raw chicken bones (I buy wings and use the carcasses of chickens that I have portioned myself). OR you can use the bones from a roast bird - it's up to you, but whatever you do, don't use a cheap supermarket chicken to make stock with - their bones are underdeveloped and the stock is always weedy, even after boiling down.
Okay - stick the bones in the biggest pan you have, along with a peeled onion or two (cut in half), some celery stalks cut into chiunks, a couple of peeled carrots, chunked, a couple of bayleaves and a few peppercorns. cover the lot with water and bring to the boil, skimming off the scum that rises to the top. When the water has come to the boil, turn the heat down to a very low simmer - if you continue to boil it, the fat on the carcasse melts and goes into the stock, and makes it greasy. Cook for about three hours, lid off. After three hours, strain through a colander or sieve, discard the bones and veg and return the stock to the pan. You then boil it like mad until it reduces to about a third of its original volume. You now have chicken glace, or strong chicken stock. Pour into a suitable container and leave to cool. You can freeze it. you can use it 'neat' or dilute it to taste. I make it every week and always have it in the freezer. I learnt how to make it at cookery school and I think everyone should do it - down with OXO!