Learn Croatian: Jesi li završio projekt? Naravno! - Did you finish the project? Of course!

In Croatian, the past tense is made of two parts: a helper verb and the main verb. Here, the helper verb is Jesi (the "you" form of "to be") and the main verb is završio (finished). To ask a yes/no question, you simply put the question word li right after the helper verb.

Why does the verb završio end in -o?

In the past tense, the main verb changes depending on the gender of the person doing the action. The -o ending tells us that the speaker is asking a man. If they were asking a woman, they would use the feminine ending -a, making it završila.

Projekt is the direct object of the sentence. Why doesn't it have a special ending?

Direct objects do take the accusative case, which often changes the end of a word. However, for masculine nouns that are non-living things (inanimate) like projekt, the accusative form looks exactly the same as the basic dictionary form. So, it doesn't change!

Where is the word for "you" in this sentence?

Croatian usually drops subject pronouns like ti (you) because the helper verb Jesi already makes it perfectly clear who you are talking to. You could technically say Jesi li ti završio projekt?, but leaving the pronoun out is the standard and most natural way to speak.