Learn Hardcore Croatian: Odmah zatvori vrata, molim te. - Close the door right away, please.

Zatvori is an imperative (command) form of the verb zatvoriti (to close / to shut). In Croatian, imperatives are used a lot in everyday speech for requests and instructions. Here it’s a direct command/request: “Close the door…”.

Who is being addressed—why is it zatvori and not some other form?

Zatvori is the imperative for ti (you, singular/informal).
If you were speaking to:

one person formally (Vi): Odmah zatvorite vrata, molim.
multiple people (vi plural): Odmah zatvorite vrata, molim.

What does odmah add—does it just mean “now”?

Odmah means immediately / right away. It’s stronger than just sad(a) (now). It adds urgency: not just “close the door”, but “do it right away”.

Why is vrata plural—does it literally mean “doors”?

In Croatian, vrata (door) is a plural-only noun (like “scissors” in English). So you say:

= “the door is closed” (literally “the doors are closed”)