The Lesson Button element is available when you are editing a Lesson in a OptimizeMentor Course. This element will not be available on other pages or 3rd party course builders.
The button will be a "Complete" button, and then will turn into a "Next Lesson" button once the lesson is marked as completed.
When adding the Lesson Button, you can click the Lesson state and choose "Complete Lesson" to edit the button text for "Complete" and also choose whether to automatically go to the next lesson or not after marking the lesson complete. By default it would just refresh the page and then show a next button.
If you choose the "Next Lesson" Lesson state then you can edit the text on the button for that state. By default it sets the text as "Next"
The purpose of this Lesson Button element is to simply provide a means of lesson navigation in order to avoid having to get the lesson link and manually putting it into a button, and of course the best part is we now have a "complete" button, which also marks the lesson complete, and will show the progress for the course if you add the Course Progress bar element, which works just like the Progress bar element, only the completion percentage is linked to the Course and is calculated by the number of complete lessons.