Ok, so... I'm new to wearing cock rings, too, but here's what I have experienced. First, I went to Canadian Tire and bought some stainless steel harness rings for about $2.50 - $3.50.
Why wear them? It feels like someone has their hands around or on my penis/scrotum.
I've found that:
A 1.25" ring fits on the shaft as far as it will slide next to the scrotum, and hasn't fallen off yet. It holds the blood, but in a pinch, I can still work it off while I have an erection. It makes for a very hard erection, till you feel your glans getting cold. Once, outside on a cold day, while wearing the 1.25" under my clothes, I felt it slip off my glans. I caught it before anyone around me knew what had happened. I've ordered a 1.125" ring to see if that'll fit the glans/head better. There's no way that the 1" they sell for this purpose, would fit...and I'm not going to try. If I have my clothes off (nudist), am wearing a kilt or simply not wearing pants or out in the cold, I think the 1.125" will be perfect.
I tried a 3" plastic ring around my penis and scrotum/testicles. Of course, it fit large, but did hang a bit too low, so I used a couple of those wrist bands from various charities (2.5" stretch material?), and they fit great, and if need be, can be cut easily. Three of those that I have, are glow in the dark ones for Hallowe'en.
I actually shoot further if I'm not wearing a cock ring. I don't have ED, so I don't need it for coitus. When climaxing with the ring on, the semen just seeps out...it's not as enjoyable.
Ok, so I got the courage to try a 2" stainless steel ring from Canadian Tire... about $3.50. People are right. To put them on, put one testicle through, pull the scrotum gently and the other will follow. Once you have both testicles through, you can bend the penis through...but....
Getting it off has to be in reverse. First I thought...sh*t. I can't get this erect thing out of the ring...Oh Oh... but I found from a fully on position, I can slip one testicle through, gently pull the scrotum and the other testicle can be guided through the ring allowing the ring to slip off the penis.
I've found that the 2" fits snug enough to feel great, but it doesn't cut off blood flow to be dangerous. I actually use it for decoration/jewelry. I've ordered a fancy one 2.125". I'll see how that goes before ordering a fancy 2" later. I know, a true nudist doesn't draw attention to himself, but if the ladies are dressing in their "slut" "club" wear, what is a guy supposed to do?
I guess my suggestion, is to order or buy some inexpensive rings, try them out, start large and downsize once you've tried them out. I've ordered some rubber coloured rings, too. They can be cut easily if necessary.
Now, I wear the large ones around scrotum and penis (2"), on the shaft (1.25") and on the glans (1.125").
Enjoy!