The United Nations Food and Agriculture Organization has produced an excellent self-instructional module on Digitization and Digital Libraries, which includes a unit on Greenstone.

Building collections on a remote Greenstone server. This scheme allows users to augment and edit collections that are held on a remote Greenstone server. Users work with a modified version of the Greenstone Librarian Interface but do not need to have Greenstone running locally. Multiple users can collaborate on the same collection (though not at the same time). Here are details of an experimental version that you can download (En Español).