Watch the following video first, reading the captions. Then start it over and paint along on a piece of watercolor paper (if you don't have watercolor paper, you can paint in your sketcbook, but it doesn't work as well.) If you want to pull out the piece and use removable masking tape or washi tape along the edges, you may.
You can choose your own colors from your watercolor set. Just be sure to pay attention to the values, working light to dark. Do not use white. You change the value of a color using more or less water in your brush.
Art Appreciation Homework
You'll love this video about a 16 year old artist! No questions to answer, just enjoy.