What does the left side of the heart do?

The left side of the heart pumps oxygenated blood to the body.

See the picture below, that's the heart.

Look at the left side of the picture, and now look at the right side of the picture. What do you see that's different?

One side looks a lot thicker than the other. The side that is thicker is the left side of the heart. The thickness of that muscular wall helps pump the blood to the rest of your body.

How blood moves and the left ventricles role:

The heart is made up of four chambers. The blood flows into the superior vena cava which is a vein, and flows into the right atrium.

From the right atrium, moves into the right ventricle, and moves to the lungs through the pulmonary artery to get oxygen. After it becomes oxygenated, it moves back into the left atrium from the pulmonary vein and then goes into the left ventricle.

From the left ventricle, the blood carrying oxygen gets pumped into the aorta and exits the heart.