Learn Hardcore Russian: Мой друг изучает музыку.

Изучает is the third person singular form of the imperfective verb изучать. It is in the present tense and indicates an ongoing or habitual action of "studying" music.

Why is the possessive adjective мой used with друг instead of a different form like моя?

Russian adjectives must agree with the noun in gender and number. Since друг (friend) is masculine singular, the correct possessive adjective is мой. If the noun were feminine, you would use моя instead.

What case is музыку and why does its ending change from музыка?

Музыку is in the accusative case, which is used for the direct object of the verb. For many feminine nouns ending in -а, the accusative singular replaces the ending -а with -у (or -ю), so музыка becomes музыку when it is the object of the action.

How strict is the word order in this sentence, and can it be rearranged without changing the meaning?

While Мой друг изучает музыку follows the typical Subject-Verb-Object order in Russian, the language’s word order is quite flexible. You could rearrange the sentence (for example, Музыку изучает мой друг) to emphasize different parts, and the basic meaning would remain clear.

Why doesn’t the sentence include an article equivalent to "a" or "the" as in English?

Russian does not have articles. The language relies on context and word forms to convey meaning that English often shows with "a" or "the", so no such word appears in the sentence.

Could another verb be used instead of изучает to say "studies music," and what would the nuances be?

While Russian does have other verbs related to learning, such as учиться, изучать specifically implies a systematic or in-depth study. Using изучает indicates that the friend is engaging with music in a detailed or structured way, rather than just casually learning it.