wow! you're brave! a tiered cake is quite high tech for a beginner. You'll need to support the layers even if the tiers are on top of each other. Roll out icing is easiest, and you can colour that and cut out shapes to decorsate with that too. Google images is great for inspiration
You need roll out fondant/royal icing from supermarkets. You cna buy it ready rolled if youa re feeling ultra lazy, get one pack per layer. Cook and cool cakes, then slice tops to make them level. Brush over with jam or cover in thin layer buttercream to make it stick then lie fondant over top and smooth.
That is basic basic though, watch vids here, here and google 'covering cakes with fondant icing' and 'decorating with fondant icing'
You can use chopsticks as supports...stick it through bottom layers and then have about an inch at least going into top cake level.
You need thin boards for each of the top layers, and you need either plastic dowels or chopsticks in each cake too, to support the weight of the one above it. Cut them to the depth of your baked cake and stick three in the bottom layer and three in the middle layer to hold the one above it up so they don't sink into each other.