There are plenty of different ways to use a cock ring. Some people enjoy using them as part of bondage or orgasm control; a tight ring applied before the cock is erect can provide some fascinating sensations once it's hard, though it's important to be careful not to use one that's too tight. Others use them more as a method of introducing something else for their partner - you can get pleasure rings that come with attachments designed to penetrate a partner's anus or stimulate their clitoris. Most, though, are simply about heightening the wearer's pleasure; they come in varying widths and thicknesses, and many of them vibrate. Penis rings can also help many people to attain and maintain an erection if that's something they can have some trouble with.
In some countries, of which America is a major example, circumcision at birth is the norm for babies who are born with penises. This isn't true in most parts of the world (in the UK, for example, circumcision is generally only carried out for medical or religious reasons) but it does mean that there are places in the West where coming across a partner with an uncircumcised penis (or an 'uncut cock') is comparatively rare.
It's not actually the case that circumcision is essential for good health and hygiene, and there are some pretty significant drawbacks to the procedure - such as the fact that it can decrease male pleasure. It's certainly the case however that for many people a cut cock is more aesthetically pleasing, and those who are used to seeing them may come to fetishise them over time. Whatever turns you on is okay, of course, but you must remember not to body-shame people alongside your kinks and fetishes! All cocks can be fantastic cocks, no matter their circumcision status.
Adorable comedy duo Garfunkel & Oates have a song the chorus of which begins with "Hand-job, bland-job, I-don't-understand-job". It's a reasonable point: giving a handjob can be a bit daunting for people who don't themselves have penises, particularly because a lot of people who do have learned over the years that they're probably better off doing it themselves!
The good news is that this is surmountable. If you are yourself possessing of a penis, spend some time figuring out what you like and don't be afraid to ask for it clearly. If you're the one trying to give the handjob, remember that everyone is different and make a point of asking your partner what they like the most.