Fondant does not dry as hard as gumpaste. It depends on what you want to make, which one you use. For instance, you would never cover a cake with gumpaste as the covering would be rock hard after it dries. Fondant will dry to a certain extent, but it does remain somewhat pliable. Sometimes, depending on what you want to make, you can mix the two 50/50 and get the benefits of both. I've made some flowers using the mixture. But I've also made flowers using one or the other. While gumpaste is edible, most people would say they wouldn't eat it - it's too hard to eat once it's dried. Fondant, however, can be eaten, and if it covers the entire cake, it can be eaten. Some people wouldn't eat fondant, though, if it were a case of eating a fondant rose, for instance. It's OK as a cake covering, but to sit and eat a fondant flower or bow ... you could, but many people wouldn't.
Hi and Welcome, Rosie932. 
Decoding CC acronyms:
http://forum.cakecentral.com/cake-decorating-ftopict-2926-.html
Cake baking & decorating terms:
http://www.ladycakes.com/CakeDecoratingTerms/cake_decorating_terms.htm
HTH
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