The phrase vamos embora evolved from the old time phrase Vamos em boa hora. Say it fast! Meaning, let’s go at a good time (while spirits are high!). It’s current meaning is roughly: go away, leave.
Vamos embora logo. (Let's go soon.)
It’s often used with the verb ir like this:
Eu preciso ir embora. (I need to leave.)
Ele vai embora. (He's leaving.)
Ela foi embora. (She left.)