Your bookmarks are visible only to you, and serve as a quick reference in your Tettra sidebar.
You'll only see a Bookmarks section of the sidebar if you have already bookmarked content.
Here's how to bookmark a category:
Step 1. Go to the left sidebar and click the category you want to bookmark.
Step 2. Once inside the category, click the kebab menu on the upper right side and select Bookmark.
You'll then see the category in the left sidebar under Your bookmarks.