Questions & Answers about Ispred vrata je neki čovjek.
Why do we use neki here instead of netko (someone)?
Neki is an adjective meaning "some" or "a certain", so it describes the noun next to it (čovjek). Netko is a pronoun meaning "someone", used entirely on its own. If you wanted to say "Someone is in front of the door", you would drop the noun and just say Ispred vrata je netko.
Why is the verb je placed right after Ispred vrata instead of next to the subject čovjek?
Je is an enclitic (a short, "weak" word), and Croatian grammar requires enclitics to sit in the second position of a sentence. The phrase Ispred vrata (in front of the door) counts as the first chunk of information, so je jumps into the second spot right after it.
What case is the word vrata in here?
It is in the genitive case because the preposition ispred (in front of) always forces the noun that follows it into the genitive. The word vrata (door) is a plural-only noun in Croatian, and its genitive form happens to look exactly the same as its dictionary form.
If vrata is a plural word, why do we use the singular verb je (is)?
The verb agrees with the main subject of the sentence, which is neki čovjek (some man). Because "some man" is singular, we use je. The door (vrata) is just part of the location phrase describing where he is!