The real origin of this word has to do with law. In the 50's or sometime
back then, it was very common for there to be abuse and such in households. In a court of law, this topic would be known as "filed under carnal
knowledge"
Eventually, this word became and acronym and was just called "fuck". Nowadays however, fuck takes many different meanings. Here are three examples.
1)sex
2)a way of expressing anger, similar to shitand oh no
3)an insult, like calling someone an asshole.