The user manual for Corona can be obtained from here. This document provides a walkthrough how to setup and use Corona.
The developers guide for Corona can be obtained from here. This document provides technical information about how Corona works internally, and provides instructions and walkthroughs on how to modify and extend Corona, as well as how to build a new frontend to a Corona server.
The generated Javadoc for Corona can be downloaded from the downloads page as a JAR file. Alternativly, you can view the Javadoc online here.