Firstly, your English isn’t dumb. You are doing great.
So, in the USA we have The Constitution, which is basically the Most Important Laws. Any other law we pass cannot go against what the Constitution says, and, while it is possible to change The Constitution, it’s very hard to do, and it rarely happens.
In The Constitution there is a law written to allow people to have guns. In large part, this is because society was very different when it was written. But, we haven’t changed the law. As I said, that’s very hard to do, and in the USA there is an attitude that you have to really have a very important reason to change The Constitution. In some ways, it is almost treated as a religious document here.
It is illegal for people who are criminals to buy a gun, though, and there are lots of other restrictions too. Most people support those restrictions, and many people would like to see there be more restrictions. A very few people would like to see guns be outlawed in this country, much as they are in China. And another very few people would like it if anyone could have any gun at any time. But most people here are ok with civilians (people who aren’t police or military) having guns, as long as they are safe about it. There is a lot of discussion in the USA about what restrictions are good, and which go too far, so there will be lots of people arguing about that here too. It’s a topic that people get very angry about.
If anyone in this country uses a gun and hurts or kills another person, or even threatens them, they get into a lot of trouble. Despite what you see on TV, everyone doesn’t have guns and runs around shooting them.
I don’t know much about nuclear weapons like you mentioned, and I’m not sure they exist, but people here would not be allowed to have something like that. Mostly the USA is pretty safe, and you really don’t have to worry about the guns, even though it comes up a lot on TV and in discussions.