How do I adjust measurements when substituting active dry yeast for compressed fresh?

Someone gave me a bread recipe book (I'm a novice baker) and, while the recipes look delicious and easy, they all call for a type of yeast I don't have easily on hand: "compressed fresh yeast." I do have Active Dry Yeast (I use it for making pizza dough), and the author says it is possible to substitute ... but he's not very clear on exactly how to do it. He says, "all recipes use compressed fresh yeast, so if you are using instant or dry yeast, reduce the quantities a little." Most of his recipes call for either "1 package" or "1 oz./30g" of yeast... others call for "2 cakes" or sometimes "1/2oz. = 15g package." My Fleischmann's yeast comes in quarter-ounce packets and I also have a 4-oz. jar of it. How should I work the equivalencies? And, do I need to mix the active dry yeast with water and sugar before adding it to the bread dough? Thanks.