I Couldn't open up your mb file properly since I'm using version 4.5 and you're on 5. I'm not sure what the problem you're having is. When you start building shading networks, you're going to find that you'll have to go back and fiddle with material attributes and whatnot. The best way to learn is to start tweaking and undoing. As kb likes to say, "Do a lot. Fail a lot. Learn a lot."