1.A piece of cake
It means something easily done
E.g. Mathematics homework is just a piece of cake to me. I can finish it within 15 minutes.
2.In a nutshell
It means in a few words, briefly
E.g. My mother replies me in a nutshell without reasons that she will not take me to the zoo this weekend.
3.To spill the beans
It means to reveal a secret
E.g. My teacher is supposed to announce my score in examination a few weeks later but she spills the beans today that I score 80 in English!
4.Not my cup of tea
It means something that you don’t like
E.g. Steak and Pork are neither my cup of tea. I like vegetables the most.
5.Bad apple
It means a bad or corrupted person in a group
E.g. Don’t make friend with bad apples! Their misbehavior will easily lead you to go astray.