The difference between categories Fiction and Fan Fiction is likely to confuse, well, every human human, so
the Fan Creations Wiki us saddos will explain how to and help you determine which of the two your article is in.
Fiction is basically how it is IRL. Think fiction books, they were made from scratch with no supporting basis at all, right? For example, Harry Potter was built out of a sudden "hey! That's a good idea!" by the author, J.K. Rowling. Fan Fiction, on the other hand, builds on things that already exist, such as an abridgement of a Harry Potter book, or something along those awkward lines—however, if I combined the two, such as having a character in a series based on Harry Potter, i.e. a guy called Bob in a fan-made Harry Potter book, "Bob" would still be classified as Fiction, because you created it yourself from scratch, basically.
In a lesser detail albeit easier format;