People sometimes call each other "dude" in casual conversation. For example:

A: Dude, we've got to get going. We're going to be late.

B: Dude, chill out.

"Dude" is mostly used between two young or middle-aged men. However, women sometimes use it and people sometimes use it toward women too. Originally, "dude" was associated with surfers. In the past 30 years it has become much more common, but now some younger people choose other words to refer to each other like "bro".

People mostly say "Dude" at the beginning of a sentence. It's possible at the end of a sentence but less common.

Nice shot, dude.