Documentation is divided into a few categories, such as "Email", "DNS", and "Database", which covers the common types of service you'll be managing with your Virtualmin installation. Within each category you'll find a few types of document, such as "FAQ", "Troubleshooting", and specific task guides.
Pages labeled "FAQ" or "Frequently Asked Questions" are intended primarily for common questions new users, or potential users, ask about Virtualmin and the services it manages. For example, the FAQ for Email includes a brief, non-technical, description of the email processing stack in a default Virtualmin system. The FAQs are generally non-technical in nature, and do not generally provide solutions to problems. They are conceptual and broad, merely to describe the way Virtualmin does things.
Pages labeled "Troubleshooting" are intended to help you solve specific problems. If you are receiving an error message from a service or Virtualmin, the troubleshooting section for that particular service may have solutions. For example, the Web troubleshooting guide includes solutions to many problems relating to problems running applications, error conditions, and VirtualHost related anomalies (such as the wrong site showing up, or confusion about "default" websites). Troubleshooting pages are specific and technical, and are intended to help you solve problems.
Documentation is tagged with the projects or products to which it applies. A few features in Virtualmin and Cloudmin only apply to the Professional version of the product, and they will be tagged with "Virtualmin Pro" or "Cloudmin Pro". Features that apply to both products will be also be tagged "Virtualmin GPL" or "Cloudmin GPL".
You can also search just the documentation by opening the search form and using the Advanced Search form to search within content "Only of the type(s)" and choosing "Book page".
The search page, by default, searches all of the content on Virtualmin.com, including forums, issues, and documentation. This may, or may not, be what you want, depending on the questions you have.