On the Go Menu, click Table of Contents (shortcut C), or click the 
button on the toolbar.
This brings up the project's main table of contents in the index pane.
See also
- Going to the home page specified for the index and content panes
- Setting the home page
- Showing thumbnail images in the index pane
- Synchronizing the table of contents to the topic in the content pane
- Viewing the table of contents in tree format