There are two separate levels of Government in America.
Our states are almost like separate nations. Our Federal Government (In Washington DC) is responsible for the military, immigration laws, printing money, and handling disputes between the states.
And our 50 states pass and enforce laws against murder, arson, robbery, and other similar crimes. The states are supposed to handle education, run prisons, build roads, etc. The states and the Federal government are separate. Governors and representatives are elected by people in that state, not appointed by the Federal government.
But our Federal Government often takes power from the states and does things themselves.
Laws about firearms vary from state to state. I live in Alabama and in my state it’s legal to own and shoot a semi-automatic rifle, including an AK-47 or AR-15. Of course we can’t just walk around in public with a rifle because it would scare many people.
In my state a person who has never been a criminal can easily get a permit to carry a pistol concealed too. Our police think that if the people are armed then criminals will be afraid to attack anyone. The pistol has to stay hidden so that no one gets scared though…
But in other states there are laws against owning rifles and handguns. In some states it is very difficult or impossible to legally own or shoot many kinds of guns, probably harder than it is in parts of China.
Our Federal Government passed a law in the 1930s that all full automatic weapons had to be registered and that only people who passed full criminal background checks could ever be allowed to own them.
Then in 1986 the Federal Government passed another law that banned anyone from making a new machine gun or full automatic gun. The ones that were already made were still legal. Federal law says that the receiver with the serial number is the actual weapon though. So it’s ok to replace parts that wear out. But you can not convert a semi auto to a full auto without breaking the law, and going to jail for a long time.
There was another gun control law that banned the new manufacture of large magazines and some semi automatic rifles. But part of that law was that the law would go away in 10 years unless Congress renewed it. Congress didn’t have the votes to renew it so that law has gone away now.