How do vacuum pumps work?

Vacuum phenomenon. By placing a tube over the penis and drawing negative pressure, blood is pulled into the penis's cavities and an erection occurs. A constricting band is deployed over the base of the penis trapping the blood and sustaining the erection. When no longer needed, the constricting band is removed and the penis should return to the flaccid state. Just physics. Hope not to leave you up in the air!
For what. At your age i can think only that you mean penis... Right? This is a temporary remedy as the pump will increase the circumference of your penis as the vacuum will engorge the organ with fluid by the action of the vacuum pump. After a short period of time it will resume normal size leaving possible behind a blue penis ( bruises). Good luck if this is what you want....