Learn Croatian: Slušaš li glazbu? - Are you listening to music?

The dictionary form of the word for music is glazba, which is a feminine noun. In this sentence, music is the direct object (the thing being listened to). In Croatian, feminine nouns ending in -a change their ending to -u when they are the direct object. This grammatical form is called the accusative case.

English says "listening to music". Why isn't there a word for "to" in the Croatian sentence?

The Croatian verb slušati (to listen) takes a direct object directly, without needing a preposition like "to". You literally say "listen music" (slušaš glazbu).

What is the purpose of the word li in this sentence?

li is a tiny question particle used to ask "yes or no" questions. A very common way to ask a question in Croatian is to put the verb first, followed immediately by li. Here, slušaš means "you listen", so Slušaš li means "Do you listen?" or "Are you listening?"

Where is the word for "you"?

Croatian often leaves out subject pronouns because the verb ending already tells us who is doing the action. The -š at the end of slušaš tells us that "you" (singular) are the one listening, so the word ti (you) isn't needed.