Explain (in your own words) how blood flows through the heart and throughout the body.

Blood flows through veins and white blood cells carry oxygen

(Well, these aren't your words but who cares?)

Oxygen enters the lungs, and enters the alveoli. These tiny organs transport oxygen into red blood cells. These red blood cells move around the body transporting oxygen and nutrients to all the cells including the heart, which pumps it around. It picks up waste from the cells and the lungs breathe that waste out.