How do I stop my fondant cracking please help and where should I store a cake once covered in fondant

Gee Kezzie, we need some more info:

what kind of cake and icing is under the fondant

what kind of cake board is under the cake

what kind of fondant and how did you roll it out

is the cake tiered and did you use proper supports inside

was the cake frozen or chilled when you put the fondant on

W/o seeing exactly what you are referring to I believe this is what's called elephant skin. It usually is caused by the fondant being dry &/or old.
A cake covered in fondant can be left at room temp OR frozen for longer storage.