Ok, sorry for taking so long to get back to explain... been a bit distracted.
So its pretty simple really:
1: Each Culture has a Resource, a World Wonder Birthplace building, a Culture Style (like a temple but represents a local community really adopting in the culture in its ways and styles), and a Cultural Seed building that represents the deepening national adoption of the culture to the extent that it has become more and more a part of the fabric of the people such that even when trading, its possible to identify traits and share those cultural traits abroad.
In otherwords, to birth a Culture (aka build the World Wonder that starts a given culture):
- A city must exist in a nation that has access to the culture resource that our newly birthing culture is an evolution of. (some of the beginning cultures wouldn't have these requirements but you'd only be able to build one at a time.)
- The same city must also qualify on the basis of a number of creative and well rationaled factors such as we have now but not limited just to resources and region but also to present religions, technologies, etc...
This World Wonder gives your nation 1 of the Culture resource. You wouldn't want to trade this off right away.
Then you may now, as a result of having access to the Culture resource, build the Culture Style building in any of your cities. This building gives access to the UUs and UBs and the Heroes of the culture when otherwise technologically accessed.
For every 3 or 5 of these Culture Style buildings you build in your empire, you may also build a Cultural Seed building (much like a Cathedral). It could maybe add an additional trade route for tourism perhaps, as the city has become well known for its donations to and preeminence among its cultural heritage (like Vienna, Paris, or New York). This building also gives your civilization an additional Culture resource.
Now you may begin to trade off your culture resource for profitable gain and diplomatic benefits. Obviously, those civilizations you are trading such a culture to may then build the Culture Style buildings in its cities and cultural seed buildings as the influence of that culture grows in its empire, then trading it off even further.
While there's more to say, I'll let that stand for now.