I am not quite sure if you are serious about all the questions here, but... I will try to help you and other that wonder about this.
Now, first I never use a ring for masturbation. A quick jack-off takes just a few min., so
I don't know what sites to look at while trying it. Maybe TeenFuns?
You get cock rings in different materials. I use to have a rubber type, but did not like it! Difficult to get on and worse to get of my cock! And it broke the first time I used it!
Now I have a leather ring that you can adjust the size after your penis. But if your penis is very thin, I don't think this one is for you. But from medium to huge, this is perfect!
It is also very comfortable to wear! It has a button lock, so it makes it easy to take on and off! And it wont brake! For a penis ring it is relatively expensive. I paid about $40 for it. But worth the money!
The purpose of the ring is to keep the blood that is pumped into your penis, in your penis. This give you a longer lasting erection and a better feeling when fucking! I also think the orgasms are better when using the ring. Just be careful not to wear it too long! Maximum time is 4 hours. If you combine the ring with viagra you can get a very long lasting erection (seldom, I think). If it last more than 4 hours you can do damage to your penis, so contact a doctor!
Buy one and try one! I am sure you will be happy with it! But keep in mind; -you get what you pay for!