Technically all protein in general is needed to build muscle. Yes, you do need protein to build muscle which, being more dense than fat, in turn can increase your weight. However, your diet and excercise will determine how much weight you will gain. Just taking protein supplements alone will not help in lean muscle gains. This is a very good quality protein and IMO the best bang for the buck and you should always have some on hand. Your total protein intake to gain lean muscle should be between 1.0-1.5 grams of protein per pound of body weight. And it is ideal to take that amount of protein in smaller proportions throughout your day (over 6-7 meals and snacks).
Yes, you can certainly take one serving of this before and you definatly will need to take one directly afterwards as this is when you need a fast absorbing protein the most. As for before your workout, a slower digesting protein is better than whey because it will keep you anabolic longer, but in a pinch, whey is better than nothing. I eat cottage cheese or string cheese and some nuts before working out instead of whey because its cheaper and the proteins are more slowly digested. If you have extra whey laying around, take it both before and after and you won't be wasting your money, however when money is tighter, you get the most bang for the buck with whey as your "first thing in the morning" shake and directly after working out. Hope this helped.