Great question. They eat... how about dirt? The dirt here is absolutely packed with bacteria.
Hah! Magic... as though that's necessary for a fantasy setting, amirite? Okay, okay, if I need magic, I'd go with something more similar to superpowers. In other words, some people are innately born with one specific power, which they can become more powerful at with practice.
City-states is a good way of saying it.
History, eh... well, there's not much. Each society is functionally at the stone age, or possibly up through the iron-age, depending on their location. They might all have their own history, but I can't imagine there being enough interaction between them to warrant a sort of world-wide history.
Now, if you're talking about how the world was formed, the implication I'm sort of going for is that it was created much like the "domains" were, with some other being designing this world merely for his or her own amusement.
Besides sustenance living? Well, I'm sure they have games, stories, possibly even written language. And of course, trade. Trade routes are treacherous, but mind-blowingly lucrative.
And don't worry! Questions are great!