What does the app do? First, you should write an overview which explains what the app actually does. Writing your idea down will help to clarify it in your own mind. Not only will this then help you explain the idea to others, but it also forces you to be a little more detailed and helps you catch points you may have missed.
Don’t try to sell the app by using lots of exciting descriptions, just keep the language plain, simple and easy to understand. Remember, not everyone reading this will be as informed as you are!
Write a detailed description of what your app does.