Well I do not know where you get three. Neither a mortgage or common stock is a derivative but 'financial instruments'. A derivative is something whose value changes upon a change in an underlyer financial instrument, commodity, or currency. You may want to visit the book "All About Derivatives"; McGraw Hill.
Joe the Plumbers loan is valued, in part by the value of his house and land, and in part by his credit record. derivative #1. Fannie bought it, and packaged it into some uber-security. derivative #2. AGNC bought it, and convinced investors to part with some of their hard earned dollars in order to own a portion of it. derivative #3. may deity forbid you using AGNC stock as margin collateral.