It's complicated.
It is also a constant, ongoing battle here in the U.S.
To break it down into real world, every day, "nitty gritty", there are some places in the U.S. that you can open carry without getting accosted by law enforcement officers, and there are other places where you will be accosted (and perhaps disarmed and even arrested). Here in rural east Tennessee, where I live, I occasionally see people open carry in public. You just best not do it inside a business or government building that has a "no handguns permitted" sign on the door. I happen to have a carry permit. My permit says "Handgun Carry Permit". It doesn't say anything about me having to conceal the handgun. Personally, I prefer not to go through the potential hassle of being questioned by the police if I open carry, so I only carry concealed.
On the other end of the spectrum, try open carrying in New York City and see how far you get, lol. ;-)
So, to answer your question, there are federal laws, state laws, and municipal laws. If you don't want to have an interaction with law enforcement officers, it's best to know the "lay of the land". ;-)
Sorry, but that's the best answer I can give.