This site does have adult content. They have cracked down in the past six months, that now if you sign up, and you are suspected of being under the legal age, you are to provide actual government proof you are the age you say you are, if you cannot, you and your stories are gone from that site.
Other than being adult content, it's an alright site. It has forums, and a catergory for each section/sub section. I myself use this site, in my eyes nothing is wrong other than the fact it's for adults. I have yet to run across someone under 18.
It's pretty self-explanatory.
Anything happens at adultfanfiction.net. Basically, people write pornographic fanfiction about their favorite characters. Whether it's slash, incest, pedo, bestiality, or legal heterosexual.
You're probably gonna see A LOT of Bella/Edward or Harry/Draco sex stories here.