I bought fondant from Walmart and covered my cake with it. I placed it in a cake container and I noticed that the fondant began to melt. Was it becuase it was in the cake container? It was my first time covering a cake with fondant. I'm practicing now for my daughter's Birthday party in August. Could it be because the fondant was from Walmart? I don't want the fondant doing the same thing the day of her party. What is the best store bought fondant to buy? Thanks!

Fondant doesn't like moisture, and fondant covered cakes should be kept in sealed plastic containers as they can't breath.  Cardboard cake boxes are best, you don't have to worry about the cake going stale as the fondant protects that.

Store-bought fondant shouldn't have been the issue.  Not sure what base you had under the fondant but anything to moisture rich wil soak into the fondant and melt it.