every time i try to put fondant on cake it cracks especially at the coerners.what am i doing wrong.and is it okay to put fresh cream frosting inside inbetween layers if am going to cover the cake with fondant.

There could be many different reasons why your fondant cracks.

-it could be too dry, try kneading in shortening or glycerin or both and see if that helps.
-the fondant could be too old, try kneading in fresh fondant
-you could be rolling it out to thick, roll it a bit thinner

these are a couple reasons why fondant cracks, there are probably other reasons too but this is what I can think of. Hopefully one of these will help you out.

And yes you can use fresh cream frosting, just remember to refrigerate it, there are some people who don't like to refrigerate a fondant covered cake due to condensation, but for me personally I've always refrigerate my fondant cakes without issues.

HTH