Add the 1 cup confectioners' sugar and beat until smooth, 2 minutes or more, adding in a little food coloring as you go. (Alternatively, you can divide the finished fondant in desired amounts and knead in gel food coloring as desired.)
Place the fondant in a gallon zippered storage bag and then in a sealed container (or at least another zippered storage bag). Store at room temperature at least 20 hours. (I stored mine for as long as 1 week prior to using it. It can last for months, really. Just reheat it in the microwave until pliable.)
To cover a cake, roll out the fondant to your desired thickness, 1/8-inch to 4/25-inch (2 nickels thick). If you mess anything up, just reheat the fondant and reroll. You want the fondant warm enough to roll quickly. You shouldn't be struggling to roll it out. If you are, it definitely needs to be rewarmed.
To glue anything to your fondant-covered cake, mix a small pinch of fondant with a few drops of water to make a runny glue. Then, using a clean kitchen paintbrush, brush the glue onto whatever you wish to glue onto the cake. Be sure to make thicker glue for heavy objects. Be sure that the item doesn't slide down the side of the cake. This recently occured to me with just one fish. It's not pretty because it leaves a shiny surface behind, similar to a snail or slug trail.
When displaying the cake, keep away from small hands that like to touch everything or you'll end up with dents in your fondant. I speak from experience.
*You will need a total of 2 tablespoons + 1-1/2 teaspoons of liquid. I suggest adding only 1 tablespoon of warm water at the beginning and then adding whatever food coloring and flavoring you desire. Be sure to measure everything as you go along. When you add a lot of food coloring, it makes the fondant way too soft to mold into shapes. Plus, it will stretch too much to put on top of the cake if it contains too much liquid. It also will depend on how long you plan on storing your fondant. If you make it 1 week in advance, the above amount of liquid is perfect. If you wish to use it right away, reduce the water by 1 tablespoon.