What is the correct meaning of- what the f*c*? Mind blowing? Head boggling? As if? গাধা hole?

There isn't really a "correct meaning," but I think it originally just meant sex. (Like, "We fucked last night.") However, the term has broadened to mean much আরো than that. It can really mean whatever আপনি want. It's a noun (like "he's a dumb fuck"), a verb ("go fuck yourself"), an adjective ("it's a fucking hellhole")... It means anything আপনি want it to mean, and আপনি can pretty much use it wherever whenever. (Just not in front of your grandmother. It IS a curse word...)