Okay kiddo, so you know how sometimes grown-ups say things to scare you, like "don't make that face or it will stay that way"? Well, this "God kills a kitten" thing is another one of those things. It's made up, not real, just a silly idea some people came up with.
The idea is that every time someone masturbates (which means touching yourself in certain ways that feel good), God gets angry and kills a cute little kitten as punishment. But that's just not true at all. There's no evidence that God has anything against people masturbating, and certainly no evidence that cute kittens are being harmed by it.
In fact, lots of people think that masturbation is perfectly normal and healthy, and even helps people learn about their own bodies and how to feel good in safe ways. So, don't worry about this "God kills a kitten" thing. You can go ahead and explore your body in ways that feel good to you, as long as you're not hurting yourself or anyone else. And if anyone tries to scare you with silly ideas like this, just remember that it's not true and keep being your awesome self.