Cock Rings
Cock rings are an exclusively male sex toy, used on the penis, fitting either at the base or around the penis and testicles. For a basically simple device they come in a number of differing designs. They may have straps of leather or cloth with fasteners, or be solid rings of rubber or metal.
They work by limiting the flow of blood out of the penis, helping to keep it fully erect. The vessels that bring blood into the penis are farther from the surface than the veins that carry blood away. The cock ring puts pressure on the surface vessels, not to actually cut off the blood circulation, but to reduce it, meaning you get a bigger, harder erection that can last longer. Also, if a cock ring also encircles the base of the penis and the scrotum, it puts pressure on the perineum, the area between the testicles and anus. This in itself can give a lot of pleasure, but it also puts pressure on the 'vas deferens', which carries sperm to the penis, delaying ejaculation. This can create a build-up to a really explosive orgasm.
Putting it On
Most of the adjustable cock rings encircle the testicles and penis. These are the easiest to put on, because all you have to do is wrap them around your cock and/or testes, and then fasten the strap. This can be a little tricky until you get used to it. While your penis is still soft, lift your balls against the underside of the penis, position the ring at the base of the balls and hold it in place with your thumb and fingers. Then release your penis and fasten the closure with your other hand. Make sure it isn't on too tightly and that you don't nip anything!
Putting on a solid metal or rubber ring is a bit harder. First grab the loose skin of your scrotum and pull it through the ring, then push your testicles through as well. Press the ring up to make space at the top, then push your penis through before adjusting the ring by pulling it back.
Flexible rings of rubber or silicone designed to fit around the base of the penis but not the balls are easiest to put on if your penis is already erect. They will simply stretch as you roll them on, a bit like a condom. These rings sometimes come with a built in vibrator, which can be used for clitoral stimulation of a partner during intercourse.
Cock Ring Safety
Cock rings do need to be used with a little common sense. Because they restrict the blood flow to a sensitive part of your body, some caution needs to be shown when using them. They should fit snugly, and have to be reasonably tight to be effective, but they should not cause pain or or bite into your skin. Use extra care when using solid rings and don't try to squeeze into one that is too small for you. They come in a range of sizes, so get one that fits properly.
As a general rule, you shouldn't leave a ring on for more than about half an hour. Don't use anything like Viagra when using a solid ring, because if you can't get soft you won't be able to get it off! If you're concerned about safety, be sure to get an adjustable ring or one with a quick release, so you can remove it easily if you think there's a problem.
Penis Enlarging
Wearing cock rings will not increase the size of your penis, at least not permanently. Some users do say that their erections with a ring seem longer and harder than normal, which does make sense due to the extra blood being held in the penis. Prolonged or regular use of cock rings will not actually enlarge your penis though. Although rings may help some people who have difficulty with erections, they will not cure erectile dysfunction problems, but feeling good about having an enhanced erection may inspire you to reach new heights.