Pausing a lesson prevents a student from accessing the selected lesson onward, while resuming it reopens the lesson. This action is available to the administrator in the student list if the student has already started learning.
To pause or resume learning, open a course and the Students tab, then select Pause Learning from the "⋯" menu (or use the group checkboxes to do the same). In the modal, select a lesson—this and all subsequent lessons will be unavailable—and confirm. A "Learning Paused" badge will appear on the student's row. You can resume learning from the same menu or by clicking the button in the modal.
A pause should not be confused with a stop lesson (this is a condition for assignments) or with the end of product access.