Home > Welcome to Moodle > Course Settings Page > Completion Tracking (tags next to assignments) > Activity Completion: Students Manually Mark as Complete
Completion tracking must be enabled for this option to be available.
This option is ideal for tracking student progression through coursework handled outside of Moodle, such as completing readings or assigned tasks. For items handled within Moodle, you might instead automate this process so an activity checks off after meeting specified requirements.