Does Whey Protein make you lean out or gain?

I bought Optimum Gold Standard 100% Whey protein yesterday after I heard several rants that it helps lean out your muscles, lose fat, and is good for post-workout. I am a woman who is trying to lose weight, and is wanting to build some sexy muscle definition along the way. Today I mentioned to some people and they said it makes you gain weight. I eat 1,500-1,800 calories daily (healthy food) and take a Woman's multi-vitamin daily. I also exercise 4-6 times a week for 30-75 minutes. With this help with my new healthy lifestyle?