What does the following code do?

CREATE OR REPLACE PROCEDURE add_new_supplier

(supplier_id_in IN NUMBER, supplier_name_in IN VARCHAR2)

IS

BEGIN

INSERT INTO suppliers (supplier_id, supplier_name )

VALUES ( supplier_id_in, supplier_name_in );

EXCEPTION

WHEN DUP_VAL_ON_INDEX THEN

raise_application_error (-20001,'error 1.');

WHEN OTHERS THEN

raise_application_error (-20002,'error 2.');

END;