Learn Turkish: Hangi evi kiralamak istiyorsunuz? - Which house do you want to rent?

Ev means "house", and the -i suffix marks it as the specific direct object (the accusative case). Because the question word hangi (which) points to a specific choice from a group, the noun that follows it must take this specific object suffix.

How does the "want to do something" structure work in this sentence?

To express wanting to do an action, you leave the main action verb in its full dictionary form, or infinitive (kiralamak, meaning "to rent"). You place it right before the verb istemek (to want), which is the only part that gets conjugated to match the person and tense: istiyorsunuz.

The verb stem for "want" is iste-. Why is it spelled istiyorsunuz with an "i"?

This is due to a pronunciation rule called vowel narrowing. When a verb stem ends in an "a" or "e" (like iste-) and you add the continuous tense suffix -iyor, that final letter narrows into an "ı", "i", "u", or "ü". Here, iste + iyor changes the "e" to an "i", becoming istiyor.

Who is being addressed by istiyorsunuz?

The suffix -sunuz is the "you" plural or formal ending. The speaker is either talking to a group of people (like a couple looking to rent) or speaking politely to a single person (like a real estate agent talking to a client).