water stains

Great website! Basically,I have just had granite countertop installed in my kitchen. The stone is golden, yellowish. The name was "Gold sand" i believe. When you drop water on it, it leaves a dark stain, which looks really bad. And now I am scared to use it so what i got from this site is that it needs to be sealed. So i called the store to seal it and they told me that they do not seal it. It has been already sealed when it comes from the factory. and one day, even one of the guys came and put some kinda polish on it, which is not helping either. I am still seeing dark stain from water. So i went back to the store and complained so they gave me  very little granite sealer "impregnator" in a bottle to apply it and told me to do it every 2-3 months or even sooner depending on how you maintain it. it sounds very soon. i have heard every six months to a year? I am really confused. it has been really bothering me. Can u tell me what exactly i should do and if that's a good sealer? or if i can use something else?

thanks