As the title say, where and how does it take its form? I get that it boils down to a group of people, a family perhaps, that establish some sort of routine and all the mannerisms a family have. Then an another family somewhere else in the same country have a different, but yet very similar traits and sort of mannerism.

Is it the environment that plays a role in how it is formed?
There has to be some common way of life that can adapt to that climate.
Take my country for example, Sweden. Often seen as a quiet people. Very introverted.
Compare that to the Americans, might be seen as more loud people and don't have any problem to talk to a stranger when that is kind of weird to do here in Sweden.

Why is that? The official theory is Sweden are like that because we have quite big landmass compared to how many that lives here. So that means far away from any neighbours and we don't have to speak to them because it is to far away. Then I think of America, giant landmass and I guess sparsely populated way back. But the majority of Americans doesn't think it is weird to talk to a stranger. (Correct me if I'm wrong, just making broad strokes here)