An extremely informal word used for a variety of purposes.
Can be used to describe love, express hate, show shock or just make a sentence seem way more fucking exagerated and fucking agressive than it need to fucking be.
person 1: "dude what the fuck was that?"
person 2: "I don't know man, the toaster just fucking exploded lol"
Example 1 - Fuck! I forgot my book at home!
Example 2 - I'm gonna fuck Lana tonight!
Example 3 - Fuck you Brian!
Example 4 - What the actual fuck is going on here?!