The sidebar provides quick access to important sections of your Discourse site. While users can customize their own sidebar to suit their preferences, providing a thoughtful default setup helps especially new users and visitors of your forum by making it easier for them to navigate.
This guide explains how to customize the existing sections and create additional sections in the sidebar. You will also learn which settings you can adjust to configure defaults for the user preferences related to the sidebar.
You can find the full guide here: Configuring the default sidebar for your users - Documentation - Disco-Docs