Keep in mind that this article refers to the "Apprentice" theme feature. We do have a stand-alone plugin as well, called "Thrive Apprentice".
One of the features you can activate in Apprentice is the "Favorites" feature:
This will add a "mark as favorite" option to the bottom of each lesson:
Currently, the favorites feature only has one option it ties in with: the Apprentice Favorites widget. Go to "Appearance" and "Widgets" to manage your widgets:
Adding this widget will show a list of favorite lessons to your logged in members, so they can easily find lessons again later.
We plan to extend the functionality of this feature in the future.