-- IN arguments : you get them. You can modify them locally but caller won't see it
-- IN OUT arguments: initialized by caller,already have a value,you can modify them and the caller will see it
-- OUT arguments: they're reinitialized by the procedure,the caller will see the final value.
CREATE PROCEDURE f (p IN NUMBER,x IN OUT NUMBER,y OUT NUMBER)
IS
BEGIN
   x:=x * p;
   y:=4 * p;
END;
/

SET SERVEROUTPUT ON

declare
   foo number := 30;
   bar number := 0;
begin
   f(5,foo,bar);
   dbms_output.put_line(foo || ' ' || bar);
end;
/

产出：150 20