Cock rings are usually made of silicone so they can be stretched over the penis and testicles to (a) help maintain an erection, (b) make said erection harder by limiting blood flow, and (c) if it has a vibrator feature, stimulate your clit during penetrative sex
Best for: Coupled penetrative sex, masturbation where you also want to focus or need more concentration for maneuvering an internal vibrator, assisting internally while your partner goes down on you.
Not great for: Just clit masturbation. They’re fine and you might like it enough for just clit masturbation, but generally speaking, you don’t want to be tied to a toy for all your clit masturbatory needs.
Tips/how to use: Try using one on your clit during missionary or doggy while your partner enters you vaginally.