Once you added the competency in the courses, open the activity settings and at last you can see the competency heading, you can select the competency you have added to the courses there and select the competency which belongs to that activity.
Whatever the scale you you it will take minimum and maximum scale only.
there is three scale means it will take 1 as min and 3 as max in yours very good as 1 and good as 2 and normal as 3. (in configure scales you may be select the required as very good and check mark across the proficient. then that will allocated to that competency.
The good may be used in further releases of moodle i think.
The above details for automatic competency completion. in case some one manualy grading means then good or normal or very good can be selected.
Grade in database is depends on the scale order (very good, good normal then grade will be vergood 1, good 2, normal 3)
Hope you have understood else revert back .