Forms :: Designing DB Application - Button Trigger?

i'm designing a DB_application where a user makes certain subject selections depending on what grades they have. so far ive made simple signin form as follows....

Create table Persons(
person_id number(8) constraint pk_Persons primary key,
person_pword varchar2(16) not null;

declare
user_id number(8);
user_pword varchar(16);
alert_button number;
begin

[code]...

now the next step... that SIGNED IN user is taken to a menu with links to select their topics or units. HOWEVER only a PARTICULAR link can be followed depending on what grade they've achieved in a NECESSARY UNIT for example to do advanced maths u need beginners maths = PASS. if = fail then user cannot proceed. heres my sql as well as the trigger ive made an attempt at...

Create table Grades(
grade_code number constraint pk_Grades primary key,
grade varchar(4) check (result in ('fail','pass')),
person_id number,
unit_code number,
CONSTRAINT fk_Persons FOREIGN KEY (person_id) REFERENCES Persons (person_id),

[code]...

i know my second trigger is poorly designed and lacking.