introduce (someone) to (someone)

When you "introduce" a person, you explain who they are.

To talk about introducing people, we use the form "Introduce (A) to (B)". It's a little unclear in this situation which person you're talking about, and which person you're talking to. For example:

Have I introduced you to Monica?

This means "Have I explained to you who Monica is?" but it also means "Have I explained who you are to Monica?"

We also use the phrase "Introduce ___ to each other."

I think I'm the one who introduced Bill and Ali to each other.

You know (something)?

When you want to talk about a new topic, one way to introduce the topic is with "You know ___?" For example, you can use this phrase to start telling a story:

Hey, you know that book store on 12th Street? So I was in there the other day, and I was looking for a cookbook...

Or you can use it to ask a question:

You know that time when we got snowed in and didn't have to go to school for a whole week? What year was that?

What's (someone's) story?

"What's ___ story?" is a way to ask for more information about someone who you don't know. It's like saying "Tell me more about that person"

What's that guy's story?

You use this phrase when someone seems interesting, mysterious, strange, or annoying.

You can also ask someone "What's your story?". This is a way to get them to introduce themselves:

A: So, what's your story?

B: I'm a friend of DeAngelo's.