If you want to write a story with a moral, then you have to decide what that moral will be. Once you decided this, then you will be able to think creatively how you would like to write on this topic. If your limitation is only 200 words, then you will have to be clear and succinct.
Here are an example.
If you wanted to write about the importance of generosity, then you can write a story of a man who had everything he wanted. And even though he had everything, he woke up one day and he realized that most of the stuff that he had required other people. For example, you can't enjoy tennis by yourself. You can't play baseball alone. Going to the movies, on vacations, eating at fancy restaurants alone is not fun at all. In fact, it is very sad. The moral of the story can be: greed and the outcome of it is its own punishment.
You can, of course, elaborate on the details.