The Index Entries on Page dockable window shows the index entries defined for the current active page - on each line a keyword for this page.
The Index Entries on Page dockable window gives a very direct way to manage the keywords for the current page:
There are several ways to add keywords. In addition to the one above, the most efficient way - unless you are very fast at typing - starts with selecting the text in the document you want to add to the index and then, either
In VISTA and Windows 7, the context menu support in addition to the normal Undo, Cut, Copy, Paste, Delete and Select All menu options which are only useful for non-western users. Western users should simply ignore them.