I suggest you take a look at the Documentation, this also contains samples and more technical information.
Although not advised you can alter the Dancing Goat SAMPLE site, but I would only use it to test or learn.
Cultures itself are assigned using the Sites Application. Those are bound to all content in that culture. As it would make no sense to have Russian content in a Japanese site. However you can copy content to another culture, or start of a new page in Culture B with the contents of Culture A.