The 'Grades' feature enables you to show your respondent a different result based on their score. For Example: If you add the Grade 'Excellent' with the score Range of 70% to 100% then if your respondent scores 8 out of 10 (80%) they will be shown the 'Excellent' grade.
Here is a guide to Adding Grades:
https://www.quiz-maker.com/Quiz-Help/Add-Grades