You would best investigate the CASE statement.
here is a simple explanation
My guess is you have fields - Score, Grade and Description
Grade and Description would be defined by a calculation using a case statement
Score is a number field that is entered.
Suppose that the name of the field containing each value is FIELD:
FIELD > 90 ; "Exellent(A)" ;
FIELD > 79 ; "Good(B)" ;
FIELD > 65 ; "Regular(C)" ;
FIELD > 54 ; "Bad(D)"