These are the little expressions we use in different situations in spoken English. Like Oh man Hey man Hey dude ...... They are used to absorb their attention to what you are about to say.

Oh, man! Thank you for answering my question! :)

"Oh, man!" - this one is a little tricky as it can be used in several situations. Here are a couple of examples: It can be used when you're surprised/excited/encouragement - "Johnny your Dad bought you a new bike" --- "Oh, man! Really? That's awesome!". It can be used when in disbelief/disappointment - "Timmy stole Johnny's new bike" --- "Oh, man! Are you serious?".