Please follow the documentation in doc/source/contributing.rst for a
detailed guide on how to contribute to documentation.
There are a number of issues listed under Docs and good first issue where you could start out.
Or maybe you have an idea of your own, by using pandas, looking for something in the documentation and thinking 'this can be improved', let's do something about that!
Feel free to ask questions on mailing list or submit an issue on Github.