What is the meaning of idiom tell someone

The phrase "tell someone" is not an idiom. It's a straightforward expression meaning to communicate information to another person.

Perhaps you're thinking of a specific idiom that includes "tell" or "someone". Could you please provide more context or a specific phrase you have in mind?

For example:

* "Tell someone off" means to scold or reprimand someone angrily.

* "Tell someone a story" means to narrate a tale to someone.

* "Tell someone what's what" means to give someone a firm and direct explanation of the situation.

Let me know what phrase you're thinking of, and I'll be happy to explain its meaning!