Norma,
What you need....
Fondant
Paste colour
Toothpick
Smoother
Butter cream
Icing sugar
Cake board
This is what you do....
Make sure your cake has a flat surface - ie. if needs be level off with a knife. Ifyou have two sandwich cakes, jam and buttercream them together, or if one, split in half and do the same. Spread a thin layer of buttercream all over the cake (this will take a bit of time to get it at smooth as poss). Put in the fridge to chill for half an hour or so and then do another layer of buttercream all over the cake, sounds a lot but it isn't. Put back in the fridge.
Take the fondant and knead it to make it pliable. Get a toothpick and with a dab at a time, add some paste colour, knead, dab, knead till you get the required blue. Best to wear some of those throw away plastic gloves whilst doing this. The fondant should be at body temperature - so very pliable by the time you come to roll it.
I do a dusting of icing sugar over the work surface and then start to roll your fondant, turning a quarter after each roll. Measure your cake from the bottom over the top and down again and you need to add about 2.5 inches on top of that so you know you have rolled it out enough. Just put your rolling pin in the middle and lift half the fondant over it to dust more icing sugar under and the same for the other side.
Yuo can either slide your hands underneath the fondant and lift it on to your cake or put the rolling pin in the middle and flip it over.
Once in place on the cake, smooth the fondant upwards with the palm of your hands so that it sticks to the sides of the cake and the top. If you smooth downwards - it will be dragged down and likely to crack/craze. Take your smoother and smooth upwards all around and across the top, getting the fondant as close to the bottom of the cake/board as you can so that you can start to trim the excess. Take a knife and run it all around the bottom - you might have to trim twice so that you know that you are not going to cut away too much all in one go. If there are any tiny creases, wrap a small amount of left over fondant into some clingfilm and roll it over the creases to smooth out.
Voila - one cake then ready to decorate with what ever you want.
If you are wanting to do some figures you will need to mix some mexican modelling paste with fondant - this makes them go hard so that they can be stuck on to your cake.