A nice start is to read the small tutorial. It shows the main principles to use the library.
A good reference is the Javadoc generated html, which provides an overview of the possibilities, and technical information on how to use the different classes.
More specific information is available on the wiki, but is not very well organized at the moment. It is used as a notepad for remembering and discussing implementation issues.
If you more information, you can ask a question in one of the forums. Bug reports, feature requests or comments are highly welcome. Some more complete documentation should be available on this page in future.