A metaphor is a comparison between two things without using the words "like" or "as" (because then it would be a simile). Ex: "You're a canary, I'm a coal mine" is a metaphorical statement because it compares them without using like/as. Canaries used to be brought into coal mines in the 1900s because they contained carbon monoxide in the air, which was a deadly gas, so the birds would die before the miners, alerting them that they needed to get out, so the speaker is saying that they're like a coal mine (dangerous) while the other person is a canary (innocent).
