Pull-ups are a lot more difficult than push-ups, and if you can do several reps in one go, then you have reasons to be proud. Typically, you can work out your back and biceps with pull-ups but there are variations that can help you workout other muscles in your upper body too.
If you can’t do pull ups initially, just try hanging from the pull up bar to improve your grip strength. If you have access to an assisted pull up machine, then using that to progress is great too. Also, doing other exercises like barbell rowing which work on your back can help like magic.
If you’re already a pull up pro, and can knock down 10-15 reps with ease, it’s time for you to try tougher things. You’ll get fitter in the process. But be warned, doing these without the assistance of an experienced professional trainer can lead to injuries. So listen to your body, and don’t do anything silly. But if you feel tough and strong enough to execute these movements, don’t hold back.