Idiomatic expressions are well-known phrases that are used to express an idea. The words that make up the phrase may have no apparent link to the actual meaning.
There are probably thousands of idiomatic expressions. Saying 'I want details' means you want specific information on (for instance) how to use them, what social situations to use them in, which variants of English use them, which specific words to use...
As you can hopefully see, your question really does not make sense. It would be something like saying 'I want details on Nigerian towns'.
I suggest you go and do some research, read up on some common examples, and when you have a more answerable and specific question, come back with that.