when to use Is with create procedure in pl/sql code example

Example: pl/sql procedure example

CREATE OR REPLACE PROCEDURE my_schema.my_procedure(param1 IN VARCHAR2) IS
    cnumber NUMBER;
BEGIN
    cnumber := 10;
    INSERT INTO my_table (num_field) VALUES (param1 + cnumber);
    COMMIT;
EXCEPTION
    WHEN OTHERS THEN
        raise_application_error(-20001, 'An error was encountered - '
            || sqlcode || ' -ERROR- ' || sqlerrm);
END;