If you mean the teacher's administration links, "Grades" is the gradebook which lists all grades of your students, while "Scales" allows you to create your own grading scales to be used in that gradebook.
"Standard Scales" are server-wide, i.e. they are created by the site admin and applied to all courses. "Custom Scales" can be created by an individual teacher and they will only be applied in his/her course.
Teaching with Moodle
Scales and Grades (Quiz Scores)
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