The Index Icon provides an interface for associating index keywords or named groups with specific Help topics. Index keywords are visible to the reader; only the author sees named groups. Note that the left upper pane contains the index keywords that the reader can see while the lower right pane shows which topics are indexed to the keywords. The right pane displays a sorted list of topics. The topics can be sorted and filtered in the same manner as in the Topic window.
For more information, see Building an Index.