CollectiveAccess version 0.6 is composed of a core cataloguing and data management application called Providence and an optional public web-access application called Pawtucket. (Other optional applications are coming in 2010 - see the roadmap for details). If you are starting out with CollectiveAccess, your first download should be Providence, which provides all of the "back-end" cataloguing and data management functionality you'll need to manage a collection.
Once you have a working Providence installation, you can publish your collection online using Pawtucket. Pawtucket is a generalized version of the software that runs Wir Waren So Frei, GVSU Art Gallery Online and other sites.