I have a few things of code I need help debugging but I feel that if I can get one of them running i\'ll be able to get the rest(oh how i hope).
create or replac         
        create or replace trigger deny_dec_pu before update of PU on ARTICLE
 for each row
 declare     
 erreur_pu exception;
  begin
     *insert into erreur values ('Operation de MAJ',sysdate);*
      -- this intruction is never executec why ?          
  if (:new.pu < :old.pu) then
  raise erreur_pu ; 
 end if;
 exception 
 when erreur_pu then 
  Raise_application_error(-20100, 'rrrrrrrr', FALSE); 
 end;
/
When you're getting an error, it's always helpful to specify what error.  There is a syntax error in the raise_application_error call in your trigger.  That procedure takes two arguments, a number and a string.  You are passing in a single argument that is one long string.
create or replace trigger minimumwage
  before insert or update on Employee
  for each row
begin
  if :new.Wage < 7.25 
  then 
    raise_application_error(-20000,'Pay is below Texas minimum wage!');
  end if;
end;
should be valid assuming there is a WAGE column in your EMPLOYEE table.