Cock rings typically are worn around the base of the cock and the balls. Put it on when you’re semi-erect. If you’ve got a solid cock ring, first pull the loose skin of your scrotum through, then drop one testicle through, then the other, and finally push your penis through. If you’re using a strip of material that fastens just gently lift your balls and fasten the strip around the penis and the balls, so it’s resting between your genitals and the rest of your body.
In general, it’s best to take off your cock ring after about twenty minutes. Pay attention to the penis; it should never turn cold or go numb (clear signs you’ve had the cock ring on too long). Clean it after use with a toy cleaner.