Learn German: Schließen Sie bitte die Tür!

In German, command sentences (the imperative mood) start with the verb. Because this is a formal command, we put the formal verb form Schließen right at the front.

Why do we need the word Sie here if it's a command? In English, we just say "Close the door!".

When you give a formal command in German, you must always include the formal "you" pronoun, Sie, right after the verb. If you leave it out, the sentence is incorrect. You only drop the "you" pronoun in informal commands.

Why is bitte in the middle of the sentence instead of at the beginning?

While you can start a sentence with Bitte, it is much more common in German formal commands to put the verb first, followed by the pronoun (Sie), and then bitte. So Schließen Sie bitte... sounds very natural.

Is die Tür in the accusative case here?

Yes! die Tür is the direct object receiving the action of being closed, so it is in the accusative case. Because Tür is a feminine noun, the article remains die (it doesn't change to den like masculine nouns do).