How Do You Set Up An Oracle Reports Function?

Hi,

I apologize if my questions seem a bit simple, but this is new territory for me. 

I have an Oracle report function that looks like this:

function cf_print_releases_msgFormu return Char is

begin

  if :p_print_releases  = 'N' then

            return 'Agreement effective from  ' || to_char(start_date,'DD-MON-YYYY') || '  to ‘ ||  '|| to_char(end_date,'DD-MON-YYYY' ')';

  end if;

  return null;

end;

So, :p_print_releases is an EBS parameter.  If it is N, then this message will be invoked within the report. 

1.  START_DATE and END_DATE is defined in the data model.  This function won't compile unless I declare those variables in the function.  Do I need to define those columns in the function?  How do I associate the START_DATE in the data model with the start_date in this function.