1) "None of your business": If someone asks you a private or personal question and you don't want to answer them, you can say "It's none of your business".
2) "Knock their heads off": Amaze someone, or astound them. It's like, if something is this amazing, your head will fall off from shock. :D
3) "Tear [someone's] hair out": Someone is very angry or stressed, and they're so angry/stressed that they tear their hair out in frustration.
4) "Bullshit": a response to an obvious lie. For example: "I've met Britney Spears." "Yeah, right./Whatever./Bullshit." all three responses would be acceptable.
5) "Holy Shit": a response to something new, crazy, outrageous, or just out of the ordinary. For example: "Holy shit! That guy just swallowed a live cockroach!"
6) "I'm fucking done": just like saying "I'm done" but with a negative emphasis.
The word "fuck" in English can be used as a noun (a fuck), gerund (I like fucking), verb (to fuck), adjective (She is fucking amazing), and just as an exclamation to add emphasis (for example, "abso-fucking-lutely" as opposed to "absolutely"). But it is a curse word and as such it is generally not used in polite conversation. One should probably wait to see if the people around you use it before using it yourself so that you don't offend anyone.