The index is normally used by marking an index word. This re-calculates the relevance scores of all index words and results. Results are automatically sorted by relevance to find results closely related to the marked word.
You can quickly see which results contain the marked word (because they have red relevance bars) and which ones are closely associated with the marked word (because they have long relevance bars). Note that it is possible for a result that does not contain the marked index word to be rated as more relevant that a result that does contain the marked index word.
Related Topics:
About the Index