In the grading process, you have the possibility to set score (points) for every question in a question set. In a question set with automatically corrected questions the total score is computed. In a question set with one or more manually corrected questions, the total score must be set by the grader. When the total score is set for a paper, you use the threshold values to decide the grade. They decide how many points you need to get an "A", a "B", and so on.
In question sets with manually corrected questions, you can choose not to use points. In this case you set a grade directly.