Is a jock strap comfortable?
A jockstrap definitely isn't as comfortable as boxers, or most other types of underwear. It's made to support your penis and testicles, kind of like the equivalent of a sports bra for a guy, so it's made to fit very tightly. Once you have it on and get used to it, it's not too bad though, and it feels good and secure, better than bouncing around.
Usually a jock strap is worn for sports or athletic activities (gym class, working out, etc.). Sometimes, they are worn to hold a protective cup in place, for contact sports such as hockey or baseball. These have a special pouch to hold the cup. A jock strap can also be worn to support the penis and testicles during non-contact sports and activities, such as running.