What is the REAL truth about creatine and how it effects your body?

So I read that the type monohydrate creating puts on water weight.. I have read that it does not from other sources...so how much water do you retain if any and how do you lose it....I take the gnc brand amp 189 tablets the rep told me that this type of creating retains no water but I also heard it is less effective!!! I have dropped weight and now want to put on muscle mass and build!!!! So someone with true knowledge please fill me in on the REAL truths of creatine.....