Cock pumps or penis pumps are a tool for increasing the size of the penis. Once erect, the penis is placed inside the cylinder of the pump. Then the air is sucked out using the handheld trigger or squeezable ball valve. This creates a vacuum within the cylinder which pressures the penis to expand and grow in size.
It is a good idea to put on a cock ring before using the pump. Blood flows easily into the penis, but the ring will prevent it from draining back out quickly. A larger erection is beneficial for more enjoyable sex and heightened sensation for both partners.