the way you wrote it, without comma, it is something you say when someone tells you something you don't care for, and you pretty much want the person who told you this, to leave you alone and preferably not talk to you any more. Example: A: Omg, you know Diane from accounts? B: Not sure, which one is that? A: Well, she caught her husband with another woman! B: ... So what? It's an antisocial thing to say. However, once you get a hang of it, you will be able to say it as joke. Since it's rude, it can easily be funny, if person you talk to knows you well and will understand what you mean. But forget about that for now.

So, what? Is an abbreviated to say, "So? What does it matter?", or it can mean, "I don't care."

"So what?" is a pretty blunt retort. You're basically saying, "and why is that important? I don't care."

" so what" is not friendly expression. so it is not appropriate to use it in your friends here in the internet. I think it is better to sa "OK" or better luck next time!

Could you please give me an example?