Your heart acts as a pump. The heart is like a tubular bag of thick muscular tissues having four chambers: two auricles and two ventricles which are connected to different arteries and veins.
Arteries carry pure blood from the heart to all parts of the body and veins carry impure blood from various parts of the body to the heart.
The right auricle receives blood from the body. As it contracts, blood flows into flows into the right ventricle. When this contracts, it pumps the blood to the lungs. The left auricle receives blood from the lungs and passes it to the left ventricle. This pumps blood to the rest of the body.