Start by having a one-line description saying what every file, class, method, function, etc., is for. Where needed, expand on what parameters are expected, and

Start by having a one-line description saying what every file, class, method, function, etc., is for. Where needed, expand on what parameters are expected, and give examples of usage. This is the API reference and it can be automatically extracted from the source code if it is part of comments. For a getting started / user guide, give a higher level description of how components tie together and show end-to-end usage examples. The key here is to be succinct but include all the information that a new user will need to get started. Whenever someone asks a question, this is a good sign that information should be added to the docs.