The Next and Previous buttons at the bottom of a course page will allow you to move through the course materials one unit at a time.
Once you reach the last unit in a course (or the last available unit in an instructor-paced course) the Next button will deactivate. If you are at the end of your course you can see your grading in the Progress tab.
In an instructor-paced course new contents are usually released each week. If you have not reached the last week of the course before the course end date, the Next button will reactivate on this unit once the new content is available.