How do I call a package from stored procedure?

just like any other stored procedure just prefix it with a package name, for example

CREATE PROCEDURE blah_blah_blah(proc parameters here)
BEGIN
--- some SQL
--- ...
--- call packaged stored procedure
DB_MAIL.CREATE_MAIL_FILE(proc parameters here);
--- call packaged function
ret_code := DB_MAIL.SEND_FAX(fax parameters here);
END;

: How do I call a package from stored procedure?