* "Break a leg." Literally, this would be a terrible thing to happen! Figuratively, it means "good luck."
* "It's raining cats and dogs." Literally, this is impossible. Figuratively, it means it's raining very heavily.
* "He's got a heart of gold." Literally, this isn't possible. Figuratively, it means he's a kind and generous person.
* "She's a real couch potato." Literally, she's not a potato! Figuratively, it means she loves to relax and watch television.
* "He's a fish out of water." Literally, a fish can't survive out of water. Figuratively, it means he's uncomfortable or out of place in his surroundings.
Let me know if you'd like more examples!