Question about fic?

I would really love some advice on what people think of fandom fic terms? I'm sometimes not exactly sure what flangst is, for example, or crack, or fluff. Like, is fluff people telling each other that they love them? Is crack the same as humour? I've never been entirely sure, although that might just be my usual anxieties raising their ugly head. I'm a fairly intelligent person, I should be able to figure this stuff out myself, right? But anyway, I would really appreciate a few people giving me examples of what they think of when they see the words fluff, crack, flangst, or angst.