Using the text styles in your document is how google docs knows what to put into the Table of Contents and hyperlink. Most of the time we don’t even think about the text styles and format as we go along. These can be used to speed up custom formatting within a document.
To find or change your text styles, look for the pull down list on your toolbar or under the Format > Paragraph Styles menu bar. I’ve found the easiest way to do change how they look is to “Update ____ to match”.
To insert items into your table of contents, then use the heading options instead of Title or Subtitle.
Once you have your headings set up (or at least started), then you can easily insert a TOC anywhere on your page. Place your cursor where you want to insert it. Select “Table of Contents” under the Insert menu at the top of the document. You will see a box appear on the page with hyperlinks to your headings throughout the document.
Notice that in the upper right hand corner of the TOC box, there is a refresh button. This is if you want to make changes (adding or subtracting headings from the document) then it will update the TOC listings.