We'll take a guess, based on similar patterns from known places. For example, if I heard of a new country called Bakbekistan, for example, I'd imagine that a person from that country would be a Bakbekistani. Or if I come across an (equally fictitious) place by the name of Orenia, I'd guess that its inhabitants would be Orenians.

There's a technical term, "demonym," for "the name for people from a certain place." Unfortunately, in English, as you've noticed, there are no construction rules for demonyms. I don't know why. It may be related to the willingness of English to adopt foreign words without regularization or modification. In answer to your last question, in real life we do one of two things. In print or when being careful, we wouldn't even try. We would just say "people from Norwood" or "residents of Hull." In a casual conversation we might invent one, using one of twenty or so (!) endings that are used in other demonyms, such as "-ian," or "-an," or "-ite" or "ennian," based on euphony. Typically it would be preceded by remark like "He's a whaddaya-call-someone-from-Norwood? 'Norwoodite?'" "Hull" seems like a real problem! (It's a town in Massachusetts). Nothing sounds good. I see that there's a discussion on a Facebook page for a residents of Hull, in England, https://www.facebook.com/HullItsYourCity/posts/453454788091756 which begins with someone asking "Hullensians? Hullians? Hullites? - what's the right term to use?" Replies, besides those three, include "Codhead," "Kingstonian," "Hulligan," and "we just say 'I'm from Hull.'" In the United States we really do call people from Indiana "Hoosiers," more often than "Indianans." On the other hand, I have never in my life heard anyone refer to people from Connecticut as "Nutmeggers," and I can't think of any Connecticut+suffix that would be reasonable. See https://en.wikipedia.org/wiki/Demonym for much more.