Arteries: any of the muscular-walled tubes forming part of the circulation system by which blood (mainly that which has been oxygenated) is conveyed from the heart to all parts of the body.
Capillaries: any of the fine branching blood vessels that form a network between the arterioles and venules.
Veins: any of the tubes forming part of the blood circulation system of the body, carrying in most cases oxygen-depleted blood toward the heart.
They are all similar because not only are they all connected to the heart, but they transfer blood and nutrients all around the body. They are different by where they are located and how effective their function is.
