Some painters like to do a detailed drawing first, and only once they're totally satisfied with this do they reach for their paints. You can either do it on a sheet of paper and then transfer it to the canvas, or do it directly on the canvas. There is a strong argument to be made for the fact that if you can't get the drawing right, your painting will never work. But it's an approach not everyone enjoys.
Remember a paintbrush is not simply a tool for coloring-in shapes, but that the direction of the brushmarks will influence the result. Even if you feel as if you're coloring-in a drawing, it's not the kind a five-year-old will do (not even a gifted one).
