In regard to blood circulation, if you begin with oxygen-poor blood that reaches the heart from the body and is pumped through arteries to capillaries of the lungs, complete the blood flow in the correct order:

The cycle runs like this:

Deoxygenated blood enters from the body to the heart via the superior/inferior vena cava. It goes directly to the right atrium and down to the right ventricle. From there it'll pass through the pulmonary artery into the lungs where diffusion will happen in the capillaries. Gas exchanges will occur and the blood will become oxygenated and return to the heart via the pulmonary vein. From the pulmonary vein it will enter back into the left atrium and then will give the final pump of oxygen rich blood into the aorta and then into the entire body.