"Understanding PREMIS" is now available from the PREMIS Maintenance Activity website. This document is a "gentle" introduction to the PREMIS Data Dictionary for Preservation Metadata, giving an overview of its scope and goals. It does not give enough information for implementation, but will make the larger document, i.e. the PREMIS Data Dictionary, more familiar.
"Understanding PREMIS" was written by Priscilla Caplan, Florida Center for Library Automation, for the Library of Congress. It is available at: http://www.loc.gov/standards/premis/understanding-premis.pdf
The full PREMIS Data Dictionary is available at: http://www.loc.gov/standards/premis/v2/premis-2-0.pdf