You use the whey the same way you use food. The amount that you take is dictated by how many calories you need.
It won't make much of a difference whether you use the wpc or w.p.isolate or the hydrolyzed whey on a calorie to calorie basis. Isolate does provide a higher biological value protein as well as a higher concentration of protein per serving than the concentrate. Additionally, the hydrolyzed is even more refined than both the isolate and concentrate because they break up some of the peptide bonds in the amino acid chains to make the proteins more easily digested, but ultimately, it becomes minutiae.
Without jumping to too many conclusions, I would guess that at this point in your development, it is nothing something you should be concerned with.
By the way, I'd recommend ignoring whatever they tell you at bodybuilding.com. They may perhaps give you some good advice here and there, but for the most part they are garbage.