Joomla allows you to add an article index or table of contents to a Joomla article. For example, if you have long Joomla article, you might want to spit it into smaller pages. With Joomla, you can easily do this and automatically add a table of contents (TOC) so the user can navigate to different parts of the article quickly. Usually, you would want to split the articles at headings, but you can split them anywhere you want.
Watch Joomla Video: How to add a table of contents (article index) to a Joomla article