Every time you create and/or edit a lesson you will see a series of options that will allow you to manage the restrictions of each lesson.
Only buyers can see this lesson
Checking this option prevents visitors from accessing this lesson until they buy your course. This means that visitors will know of the existence of the lesson because it will continue to appear in the listings at front but they will not be able to access it.
Limit description to visitors
Checking this option prevents visitors from accessing content up to the read more tag (Shift+Alt+T). This is a great option to show a part of the lesson that may interest the visitor and noticed him that to continue reading will need to buy the course.
Important: If you restrict the access to visitors, limiting the description will have no effect (Obviously because they will not be able to access to the lesson).
In your course submission view, in the lessons table, there is a column named “Restrictions” where can you have a quick view of all restrictions you are applying.