Data Sources
The user profiles listed in your PeopleZen Web Parts are provided by a something called a Data Source. A PeopleZen Data Source defines the source of the information to be displayed, and how to connect to that source (among other settings).
After installation, there is only one pre-defined PeopleZen Data Source available, titled (Default Data Source). You can customize it or add additional Data Sources via Site Settings / PeopleZen Studio / Data Sources. Each PeopleZen Web Part then lets you select which of your Data Sources to use (in its settings tool-pane, via web part menu / Modify Web Part).
Before reviewing its many other settings, the primary choice for each Data Source is the Connection provider setting. The currently supported choices are:
Farm User Profiles
This is the default choice for PeopleZen installations on SharePoint Server (and is not available on SharePoint Foundation).
Retrieves the farm-wide shared user profile information (which is often imported from Active Directory) stored in the current default User Profiles Service Application (SPS 2013 & 2010) / the current default Shared Service Provider (MOSS 2007).
Site User Accounts (People and Groups)
This is the default choice for PeopleZen installations on SharePoint Foundation.
Retrieves the user profile information (plus optionally groups if desired) stored in the current Site Collection's User Information List (at /_catalogs/users).
Active Directory
Retrieves user profile information stored in any LDAP-compatible directory service, such as Domino or Active Directory.
Database
Retrieves user profile information from SQL Server, Oracle or any other database accessible via OLEDB, ODBC or ADO.NET.