I now have my crock-pot 6 months. Because I don't need it as a time saver I have not used as much as I thought I would. But, it is great to make good chicken stock and I use it for that purpose a lot. I let the crock-pot do this during the night. My crock-pot is 3 liter/quart so a small one, adjust the ingredients to the size pot you are using and use your own judgement. I find it handy to freeze some of the stock in ice-cube bags for sauces.
If you do not have all the ingredients on the list...it does not matter, you also do not have to follow the amounts exactly, be creative and add other veg or more of the same, or what you have in the fridge and think is suitable for making this recipe, just let it cook slowly to get a great rich stock. Have fun with this and enjoy the result!