How do I substitute this kind of chocolate?

Hey guys, I need to know what I can use to substitute 2 squares of unsweetened baking chocolate. I have the unsweetened coco powder from Hershey's, and my teacher told me That would work, but I don't know how much to use, or if any other procedures have to be done to it. If you guys know the answer i could really use your help!=) thanks so much!