Fortunately, there are freely available table of contents templates that can be used in Google Docs. Once you have opened the template you can begin customizing the template to suit your own needs.

Google Slides is getting a refreshed collection of professionally designed templates this week, including options for business or school presentations. Make a good impression. Skip to main content ...

When you create/select a table of contents, tap the overflow menu button next to refresh for “More options.” Google is also “reorganizing the options included in the table properties sidebar.” ...