Hi @Dr-Sadeq
The 'free preview' option means, those who land on the landing page of your course, can preview the lecture before making a decision if they want to purchase your course. I recommend you enable the 'preview' option for the lectures you consider are good way to market your course.
The 'downloadable' lectures are those that can be downloaded by the student who have purchased the course, so that they can download and watch that lecture offline if they want.
Hope this helps!
