I have a "dumb" question regarding fondant. I have NEVER used this yet...but I have to for a wedding cake. Do you put b/c frosting under the fondant, or just the fondant?? Also, any does and dont's with using this stuff??

Yes, you need to put icing underneath so it will adhere. You can use any icing, buttercream recommended, or even Corn Syrup wil do, but Whipped Cream NO..

Thanks!!! It will be fun to try this!! Also, do you store this at room temperature or in the fridge??

Yes, as eve said any buttercream, cornserup, or even jam like you would use to help crums on a cake will work. If you have never worked with fondant yet, you better start practising. Are you going to use crimper to decorate, then you will have to roll out your fondant a little thick.
Hope this help.

The cake is just going to be just plain white fondant with a silver ribbon around it, so how thick should I make the fondant?? I do plan to practice this weekend for the first time.

..about a 1/4 of an inch should be fine. Any thinner then that and you have to worry about tearing it. Make sure you take pics!!!

make it 1/4 inch, i tried to be smart and get a bit thinner to make it go that bit further, it ripped up the sides and had to start all over again. Don't cheat is my advice.