SQL & PL/SQL

hi folks ,
i would like know how to create and execute a function whose return value is a table ,
am new to pl/sql ,
my statement for the function is

SELECT ct.credential_code, c.expiration_date
FROM certifications c, credential_types ct
WHERE ct.crdnt_id = c.crdnt_id
AND c.person_id = person_id;

i would like to have the result of the above query as return value for the function.

Thanks in advance ,

Ashok.c