First Normal Form: Fields are not subdividable
Second normal form: On the basis of the first normal form, the properties are completely dependent on the primary key. That is, there cannot be an attribute in a table that depends on another field. For example, in the grade table, when (user id, course) is used as the primary key, the course name cannot be stored because it depends on the course field.
Third normal form: Based on the second normal form, attributes do not depend on non-primary attributes of other tables. That is, in the user table, the department name cannot appear, but the department id should appear.