I've always just brewed the coffee that i want in the coffee maker and dumped it in the boil. I never used a whole carafe of coffee, usually only about a pint, but you can certainly put more in there, depending on your taste and how strong of a coffee flavor you want. It's kinda difficult to mess this up unless you put in way too much coffee and make it too bitter or if you dump hot coffee into the wort after you've already pitched the yeast.