One of the keys to speaking English like a native is the ability to use and understand casual expression, or idioms. American English is full of idioms. You won’t learn these expressions in a standard textbook. But you will hear them all the time in everyday conversations. You’ll also meet them in books, newspapers, magazines, and TV shows.
Idioms add color to the language. Master idioms and your speech will be less awkward, less foreign. You’ll also understand more of what you read and hear. Often a student of English tries to translation idioms word-for-word, or literally. If you do this, you can end up asking, "What could this possibly mean" This is why idioms are difficult: they work as groups of words, not as individual words. If you translate each word on its own, you’ll miss the meaning and in many cases end up with nonsense.