der Brief
letter
A written message, usually written on paper and sent by mail in an envelope.
Ich habe heute einen Brief von meiner Oma bekommen.
I got a letter from my grandma today.

letter
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letter
A written message, usually written on paper and sent by mail in an envelope.
Ich habe heute einen Brief von meiner Oma bekommen.
I got a letter from my grandma today.

There are fixed verb combinations around 'Brief' (letter): you can 'schreiben' (write), 'bekommen' (receive), 'lesen' (read), 'öffnen' (open), 'verschicken' (send), or 'einwerfen' (drop into a mailbox) a letter.
Ich muss heute Abend noch einen wichtigen Brief schreiben.
I still have to write an important letter this evening.
When 'der Brief' (the letter/document) is mentioned in connection with a car, registration, or sale, it almost always means the vehicle registration document. It is the colloquial short form.
Ohne den Brief kannst du das Auto nicht verkaufen.
You can't sell the car without the vehicle registration document.
This meaning is usually found in historical or legal texts. Words like 'König' (king), 'Adel' (nobility), 'Urkunde' (certificate), or 'Schulden' (debts) in the sentence indicate that an official document is meant.
Im Mittelalter verlieh der Kaiser den Städten Freiheitsbriefe.
In the Middle Ages, the emperor granted cities charters of freedom.
message / news
'die Nachricht' and 'der Brief' can both be a message to a person. 'Nachricht' is more general and often short; it can come orally, by phone, by email, or in another way. 'Brief' usually means a written message on paper, often in an envelope and sent by mail. The words can be confused because a letter also contains a message. But not every message is a letter. If the form is important, especially paper and mail, 'Brief' is more precise.

Am Montag lag ein Brief vom Amt im Briefkasten.
On Monday, there was a letter from the office in the mailbox.
Ich habe auf dem Handy eine Nachricht von meiner Kollegin bekommen.
I got a message from my colleague on my phone.