Besides "raining cats and dogs" what other expressions you natives hear from speakers learning exclusively through course books?
When learning a second language, expressions are always a challenge but they are much more important than most people realise, especially in everyday conversation. There are so many in every language. You can find lots of long lists on the Internet, but it is often difficult to know which are in common use and thus valuable to use, and which are rare and would sound strange in normal conversations. The whole issue of expressions is a "real can of worms".