TESOL习语-1. Piece of cake- As mentioned above 'a piece of cake' is referring to something that is very easy or doable. You use it when you find something extremely light and distressful.
Usage- That class test was a piece of cake for me.
TESOL习语-2. Break a leg- It might sound funny yet it isn't the literal meaning. Break a leg means good luck or do well. It's used as a well wish in situations that need it.
Usage- Oh! You've got an interview? Make sure to break a leg!
TESOL习语-3. Hit the books- Have you heard native speakers in your class use this idiom? If not, here's the meaning. It means to study. Baffled? Let the example ease your confusion.
Usage- I'm going to sleep for now mom. I will definitely hit the books in the evening.
TESOL习语-4. Let the cat out of the bag- Why would anyone put a cat into the bag in the first place? Well, worry not; the cat is safe! Let the cat out of the bag actually means to reveal a secret that was supposed to be kept a secret.
Usage- Let's not tell Reena, she always lets the cat out of the bag.
TESOL习语-5. Hit the nail on the head- Sounds violent, doesn't it? Hit the nail on the head is used to say that the person is precisely right.
Usage- When he said he wouldn't drink and drive, he hit the nail on the head.