It still seems to me that Washington make a law or rule, and each state either ignores it or not. I can't fathom out the logic. I know I'm a stupid English person but apart from local issues, shouldn't the law apply to everyone?
I tried to deal with this before, but I'll tackle it this time in isolation.
The USA Constitution defines rights according to three groups.
The first group contains those rights which belong to the federal government. This includes things like coining money, establishing roads, establishing post offices, to establish and maintain armed forces, and a few other things. States cannot do certain of those things or can only do them in a way approved by Congress. When the Congress passes a law and the President signs approval, then that law applies to all the states evenly (at least in theory).
The second group contains those rights which belongs to states individually. Article IV of the constitution talks about states' rights and responsibilities. Article VI establishes the hierarchy of jurisdictions that allow Congress to pass laws that affect all states AND make that law binding.
The 9th and 10th amendments to the constitution expressly clarify that there are rights that belong to the states but other rights belonging to the people. The 9th clarifies that unenumerated rights automatically reside with the people or with the states but not with the Federal government. The 10th makes it clear that Congress cannot simply step in to take rights not originally allocated to them. In other words, the 9th and 10th amendments are meant to prevent government growth and the annexation of extant rights.
There ARE those laws that get passed by Congress and signed by the President that change the scope of some laws, usually when they empower some government department to have federal scope of work and/or jurisdiction. AND there are those laws that SEEM to apply everywhere in the USA, but that get challenged in court as violating some amendment or another.
The recent furor of "concealed carry" occurred because New York ATTEMPTED to take on the right to circumvent the 2nd Amendment that is our source of gun ownership rights. The state tried to define a states' right that wasn't a states' right, I guess hoping to sneak it past someone who wasn't watching. Didn't work. California has at least 3 major gun rights laws and several minor ones that almost surely will be challenged shortly (if they have not already been challenged).