Been couch hopping since I was 19, about to rent for the first time

As the title says, I graduated yesterday and have a job lined up as a surgical assist in the big city in my state, but even when I was couch hopping I wasn’t in a city like this, the most I’ve spent somewhere with a pop of 15,000+ was to do my clinical hours. I’m from the middle of bumfuck nowhere farmland. What are some general principles about living in city life? How do I assimilate to it?? I’m genuinely kinda scared, my fiancé is used to the surroundings but I’m not, and I’m really nervous about how things looks (notably within the heart of the city, I saw people passed out on what I assumed to be drugs under the bridges - which I used about, but never actually seen in person)