One of the menu items is [H]elp. This provides context sensitive help by highlighting what it thinks is the most appropriate help item with a little book icon (the same as appears next to the help menu item).

Some controls have tool tips associated with them. If you leave you mouse pointer over them, for a second or two, the tip will appear detailing what the control does.

Before using the Librarian Interface, you should be generally familiar with Greenstone. The documentation explains some of the terms and actions available within the Librarian Interface.