Learn Arabic (Modern Standard): أسكن في المدينة.

In Arabic, you often do not need to use the separate pronoun for "I" (أنا). The verb أسكن (I live) already has the "I" built into it, shown by the letter أ (alif) at the very beginning.

How would I use the question words from this lesson to ask "Why do you live in the city?"

You would put لماذا (why) at the beginning of the sentence. To ask a man, you would say لماذا تسكن في المدينة؟ and for a woman, لماذا تسكنين في المدينة؟. The question word goes first, just like in English.

Why are there two words in English ("the city") but only one word in Arabic (المدينة)?

The Arabic word for "the" is the prefix ال (al-). It attaches directly to the front of the noun. So مدينة means "a city", and adding ال makes it المدينة ("the city").

Does the word في (in) affect the pronunciation of the word for city?

Yes! In formal Arabic, prepositions like في (in) cause the noun after them to end with a short "i" sound (called kasra). While often dropped in casual speech, the strict formal pronunciation of this phrase is "fil-madiinati".