They can be used directly in the mash, the boil, or suspended in conditioning beer like hops or spices. They should be used with restraint. Three ounces in a five-gallon batch is a good starting point. To get maximum effect in the mash or kettle, mill them as you would your grain.
There is a misperception that chocolate is fattening. In truth, the fats in cocoa butter are healthy fats. Cacao contains oleic acid, a heart-healthy monounsaturated fat, also found in olive oil, that may raise good cholesterol.