M.B.
It is actually pretty easy. Just lightly frost your cake with a buttercream frosting (or the Betty Crocker stuff in a jar). This improves the taste (because fondant really isn't all that yummy), and helps the fondant stick better. Then roll out your fondant like you would a pie crust. Make sure the circle is large enough to cover the top plus the height of the sides of the cake plus a little extra. Roll to about 1/4 inch thick. Either gently roll the flattened fondant icing onto your rolling pin or fold it in half twice, and carefully lay it over the cake. Smooth the fondant over the cake so it's even then take a sharp thin knife and trim all around the base of the cake. To finish off the rough edge either roll lots of small balls and place all around the perimeter (like a pearl necklace) or pipe frosting around it like you would see on a bakery/grocery cake.
Fondant can dry out quickly, so you do have to work somewhat quick.
And, after typing all of that I looked at Wilton's website, and they have some pretty good instructions with pictures here: http://www.wilton.com/wedding/makecake/fondant/index.cfm
Have fun!
P.S. Don't know exactly what you mean by fancy, but here is something that's actually pretty easy and looks really cool. For a tie die or marbled cake just decide how many different colors you would want to use (at least two). Divide the fondant into that many bowls and put food coloring in until you get your desired color. Roll each of the different colors into different sized balls (ex. some cherry sized, some golf ball sized, etc). Randomly put the different colored balls together in your hand and make one large ball of fondant. Don't mush them together too much or knead it because you'll end up with the colors combining too much and making one new color instead of multiple colors. Now roll it out just as I mentioned above and you have a really cute tie dye/ marbled cake. For my son I used white and royal blue, for our wedding cake we did white and ivory.
