I'm confused. How is FNAF 2 a prequel?

I don't have the guts to play the games myself, (I can't even sleep after just watching a few Let's Plays) so I just read info about the games online. I love the entire concept of these games.

But now I'm reading bits that FNAF 2 is actually a prequel to the first one. Can someone explain it to me how is it a prequel? The wiki hasn't given much info about this.

I just can't see how this could be a prequel (except the fact Phone Guy is alive and well in 2, but that's pretty much it.) so far.

In FNAF 2, the original Freddy, Chica, Bonnie, and Foxy are clearly in worse shape from the first one. This was the first thing that made me think this was a sequel. Next thing was the fact they said the restaurant was "re-opened".

That's about it so far. If any of you nice folks can explain the storyline of the games chronologically, it would be golden.