A "latecomer" student is one who joins the course when everyone else is already in session. They are granted access, their start date is recorded, and then the normal course schedule applies.
Grant access through the product or add a student in the Students tab, and for streams, assign the desired cohort. The student clicks "Start Learning" (or the administrator sets the start date). With a group schedule, lessons with a current date are already open, and future ones are closed. With an individual schedule, the countdown starts from the individual start date. Stop lessons and pauses in learning apply according to their own rules.
To connect a student after a course starts, open the Courses section and select a course. Access is granted on the Students tab or in the product access settings.