black galaxy granite help

I just had black galaxy Granite (http://tanbrown.org) installed, and (http://maplered.com) just found your site, now I am nervous about stains, oil in particular from cooking, etc.  how hard will this be to keep clean, what should I use, they said they have sealed it, I have not put anything down on it for the week I have had it for fear of scratches, etc..there is also one more thing..I had thought this would be way more shiny, but I can see a slight grey color that looks a little flat under some light, thats the only way I can explain it, it looks like water marks, but I know its not, just a way to explain, on the other side where the natural light isnt as strong you cant see this as much.  thanks,