The materials of a cock ring range from silicone to metal, sometimes even adjustable leather straps. Some have bullet vibes attached for extra pleasure! It's all depending on what you and your partner(s) are looking for.
Similar: Cock & ball rings/double cock rings. These types of rings must go on when the penis is limp! Lube the inside of the ring first, then slide the testicles in, one by one. Next, slide the penis through and adjust as necessary. Voila! While you can find these in stretchy jelly materials, most of what I've seen are made from firmer materials such as silicone and metal.
Cock cages/chastity cages
Used as added excitement for some males, chastity cages and cock cages are meant to suppress an erection and decrease the chances for masturbation. In most cases, this is used as bondage in BDSM practices. Some guys will need to wear them for days until they're allowed to remove them. Though I've never actually heard of this happening, I wouldn't be surprised if these cages were also used by religion men to resist temptation from sexual urges.