The primary source for PrimaGIS documentation is the PrimaGIS User Manual (pdf). The user manual is kept up-to-date for PrimaGIS releases, but may not be so for particular development versions in the Subversion repository.

This website contains additional documentation and practical examples on using PrimaGIS.

Josh Livni has created introductory PrimaGIS screencasts.

For configuring filesystem based data, please refer to the PCL's  Data Configuration: The Filesystem Backend document.

If you're interested in writing documentation for ZCO/PrimaGIS (installation instructions, use cases, etc.), please contact the mailing list. Your effort would be much appreciated!