The most standard way online for informing and guiding users to help them find the answers to their questions about the service/app are F.A.Q. pages.
phpMyFAQ is a pretty stable and open source PHP F.A.Q. application that has many features for building a good F.A.Q. system.
A powerful admin interface exists for managing the categories, entries, В users and also viewing the stats.
It is possible to enable users to ask or answer questions and comment to them or keep it admins-only.
There is an advanced search system empowering users to locate the related answers with ease.
Its look and feel can be customized with HTML-CSS, interface has multi-language support and all questions-answers can be exported as a PDF (with automated table of contents).
The F.A.Q. page has some ready-to-use modules like “most popular, latest or sticky questions”.