Hi, I'm sure more experienced and knowledgeable folks can give you more advice, but just to set the ball rolling:
I would say just about any kind of cake can be used under fondant except from really fragile cakes like chiffon cakes. If you're just starting you probably want to start with a reasonably sturdy cake until you get your confidence up. Obviously carved cakes require a sturdier structure.
I think the biggest thing for me when starting out was learning how to properly crumb coat and smooth the fondant.
There is a great free tutorial on Craftsy about basic buttercream skills but I found it helpful for how to tort, crumbcoat and prepare a cake for fondant. There are several great tutorials on youtube about how to apply and smooth the fondant to give a professional look.
Have fun, and don't be afraid to experiment!