Documentation and reference guides are located on the ClearCenter website. If you are new to ClearOS, first, take the time to understand the differences between ClearOS Community and Professional. It is a lot easier to start off on a ClearOS Professional free evaluation than to start over again by re-installing.
For those installing any ClearOS 6 version for the first time, please take a moment to read the Installation Guide.
Once installed and up and running, you'll want to refer to the User Guide which provides information and documentation for specific apps that can be installed via Marketplace (or CLI).
For those familiar with ClearOS (or Linux), there are a number of wiki-style guides that are targeted towards more advanced users looking to implement specific features not available through the Webconfig UI. Those knowledge-based articles are available here.
ClearCenter has created the ClearOS Enterprise User Guides and Video Tutorials. You can find these reference materials on clearcenter.com.