Hello Marta!
I know English. I will help you with pleasure. «It was raining cats and dogs" -is means that it was raining very heavily. You can also say - it is pouring. «He had a sweet tooth» - it means that a person like sweets very much and he can't live without it. Have you a sweet tooth? As for me I have a sweet tooth, I can eat sweets every day.
I know it is very difficult to learn foreign languages. We need to learn a lot of new words. I think that reading it is very useful in this case. You need to read a lot. You also can make a dictionary where you can write all new words.
What books do you read? Do you read adapted version or books in the original?
Write me if you have difficulties. I will help you!
Sorry I have to go!
Bye!