I just made my first batch of fondant the other day with a gal from my church who is a total wiz in the kitchen.
First things first when making rolled fondant:
You're going to need a Kitchen Aid mixer or some other industrial type mixer. A hand mixer will not work and you'll blow out the motor within seconds of using it. The reason you'll need a strong mixer is for the dough hook.
Take a large microwave safe bowl and grease a pretty decent layer of Crisco on the inside of it and the spoon you are going to use to mix the melted marshmellows with.
Melt a standard 1 pound bag of mini marshmellows in the microwave, along with 3 tablespoons of water and 1 tablespoon of whatever flavoring you want your fondant to taste like. (I used banana extract and it was really good.)
Pour your melted mix into the Kitchen Aid and add a standard 2 pound bag of powdered sugar. Make sure you add it slowly and use a sifter so there'll be no clumps. You'll be able to use the regular handle for the first part of the mixing process until it gets stiff. Your mixer will let you know when you need to switch to using the dough hook. Continue adding the powdered sugar until the bag is empty.
Make sure you have a little extra powdered on hand because you'll need to turn out your fondant on parchment paper sprinkled with it. You'll knead the sugar into your fondont until it gets dense and hard to work with. You can stop kneading once your fonadant no longer sticks to your hands or your countertop.
From there, is is ready to be rolled out.