What you could do is insert a table of contents on the top page and it will populate your headings and subheadings so that you can see it. But what happens when you are on page 20 and want to get back to the top? The Blendastic-Bombastic Personalized PD team puts links to the table of contents in the footer so that you can easily click back to the table of contents. Brilliant idea if you ask me.
If you don't want to go through the process of navigating the links, the Table of Contents add on allows you to see the table of contents to the right of your document - at all times. It also gives the option to have the Table of Contents sidebar for anyone viewing the document.
In order for this to work, you need to make sure that you have used the heading styles as you would want them to appear on your doc.
Minor HeadingGoogle docs will automatically order the table of contents assuming you have used the styles for your headings and subheadings.
When the add on window shows up, if you click on "always open for this document", the table of contents on the side will always show up for anyone viewing the document.
An example of the TOC always showing up is my Doctopus Walkthrough doc: bit.ly/doctopusaddon
Here's how it looks in a pretty little .gif: