Course completion in more detail
A look at each section in the course completion settings page
10. Grade
You can set a requirement that the course cannot be complete until a minimum grade is achieved.
If this option is enabled, and a grade is entered, the gradebook will need to be used. All assessed activities automatically go into the gradebook and the gradebook will add up the scores for a final total (using the aggregation method chosen by the teacher). The gradebook is a whole other topic!!
Once the student achieves the grade required they will be marked complete (if other conditions are also met).