I am not the English native speaker but I want to try all my best to correct your writing. I think it will help you and me Corrected from yours: "I sometimes read and hear idioms but I can't understand them. Is there a dictionary or a site which do translation or explanation meaning of idioms? If yes, what is it?" Or more polite: "I sometimes read and hear idioms but I am unable to understand some of them. Could you please let me know any dictionaries or sites which do translation or explanation meaning of idioms?"

https://www.thefreedictionary.com/

Hello, My opinion, it is difficult to understand the translation of an idiom to your primary language. A better way is to understand its meaning by explanation and its usage. To do so, just use the powerful search engine, Google. For example, I want to understand "put yourself on other shoes", I just type "put yourself on other shoes meaning" on Google then I open one of the results here.https://idioms.thefreedictionary.com/put+oneself+in+else%27s+shoes. Hope it helpful Trang

Try these: http://www.idiomsite.com/ https://www.phrases.org.uk/idioms/index.html https://www.ef.edu/english-resources/english-idioms/