Is there a way to display the hierarchical structure of a document on the left side? By structure, I mean by headings and subheadings, etc. When you click on one, it takes you there in the document. You can expand and collapse headings to show or not show subheadings. Word has this feature but I can't find it in indesign. When I google it, I just find stuff about XML.
You can use Bookmarks for this. Generate a Table of Contents and enable Create PDF bookmarks. If you don't need an actual TOC, just put it on the pasteboard, out of sight. Then double click on the headings in Window > Interactive > Bookmarks to navigate to the headings in the document.