Hi Tom! (Again!) It is an idiom meaning that one is going to do or try something, but is unsure of the outcome. I tend to use "here goes nothing" which means the same thing. For example, it is your turn to perform (a speech, a song, etc.,) and you would then turn to your friend and say it. It is typically used as an adverb, but it can be used as an exclamation. I hope that this helps you. J.