How one part of the organisms body is designed to do a specific job well ?

The #1 biology rule is that structure equals function. One part of an organism is designed to to a specific job well because of its function. For example, the heart is good at pumping blood because it has veins, arteries, and valves to assist it. The lungs would not be good at pumping blood because they lack these specific features. What a body part consists of determines what job it does and how well it does that job.

Could you elaborate?