Use the expression "Hey man" at the beginning of a sentence for a few different purposes:

• to greet someone:

  A: Hey man.

  B: Hey man. What's up?

• to get someone's attention:

  Hey man, are you finished with that?

• to correct someone's understanding of what you're thinking:

  Hey man, I didn't mean to offend you. I apologize for saying that.

"Hey man" is mostly used by men when talking to other men.