I would like to create table of contents in this github webpages site

I would like to create a table of contents on the left side of this GitHub pages site https://abenjamin09.github.io/Bellabeat-Capstone-1/. Any help would be appreciated! The section in the table of contents would ideally look like this.

Introduction

• Characters and Products

Step 1 - Ask

• List item

Step 2 - Prepare

ETC ETC

How would I go about doing this??

Thank you