A life ring is needed so that a person who has fallen overboard doesn't sink due to the weight of wet clothes while being rescued.
Nowadays they are usually made of foam, but previously they were made of cork. Modern life rings weigh 2-3 kilograms (5 - 8 pounds), although larger ones can weigh 4 or even 5 (9 - 11 pounds). Better not to get hit on the head with one, otherwise there will be no one to rescue.
Drawing it is very simple: an outer circle, an inner circle, a rope for easier grip, and bright colors for good visibility.