Of the city, of my brother (центр города)

The Of-Phrase

You already know у + Genitive for owning things: У брата есть машина. — My brother has a car. Russian has a second, even simpler use of the same case: put one noun after another and the second — in the Genitive — tells you whose or of what.

No preposition, no verb — the case ending alone does the work of English of and 's.

Order Matters

The thing comes first, the owner second: машина брата is the brother's car; брат машины is nonsense. Whatever English does with its apostrophe, Russian always says the thing of the owner.

Same Endings You Already Know

The endings are the ones this level just taught: -а/-я for masculine and neuter (город → города, море → моря), -ы/-и for feminine (сестра → сестры, песня → песни).