Headings that start topics, or to which you assign the Contents property or a contents level, are automatically included in the contents for OmniHelp; for details, see:
§16.4.2 Including contents entries in HTML-based Help.
§16.4.3 Setting contents levels for HTML-based Help.
When you click links in the topic pane while the contents pane is displayed, the contents pane stays synchronized with whatever topic you visit.
DITA2Go creates an OmniHelp index from the index entries in your DITA document. As with other HTML-based Help systems, you can specify the granularity of index-link destinations, and customize the sort order of index entries; see §16.5 Configuring index entries for Help systems.