Fan fiction is what literature might look like if it were reinvented from scratch after a nuclear apocalypse by a band of brilliant pop-culture junkies trapped in a sealed bunker. They don't do it for money. That's not what it's about. The writers write it and put it up online just for the satisfaction. They're fans, but they're not silent, couch-bound consumers of media. The culture talks to them, and they talk back to the culture in its own language. —Lev Grossman, TIME, July 18, 2011That is a great quote to explain what fanfiction is and why people write it. For most authors it's not about the money or the acclaim. It's the simple act of writing a twist in plot or a perspective you wish had happened in the fandom you immerse yourself in.
Fanfiction has been around for centuries, though not always by that name. The most observable historic form of fanfiction are unauthorized sequels to books. Sherlock Holmes stories are abundant and the Bronte sisters wrote stories about characters and people not their own. The term "fanfiction" wasn't coined until the 1960s, but the advent of the internet really let the category of writing really take off. With the internet a fanfiction could be easily spread to thousands of people across the globe, instead of being confined to a small geographical area or a small group of super-fans.
For me, fanfiction allows the continuation of the journey with characters after the credits roll or the last page of a book is read. Great fanfictions posit alternative universes where alternate decisions were made or a character is just slightly different. They allow you to jump into a story without having to be filled in on background knowledge.
As an educational tool (and yes it can be) fanfiction is a great way for students to examine a story from a different point of view or change a decision a character made and play that out. Becoming thoughtful individuals requires examining choices. Becoming good writers requires trying different styles on for size. Writing fanfiction allows for both of these things without having to develop characters, settings, or sometimes plot lines.
So where can you look for fanfiction stories? The largest repository of fanfiction is fanfiction.net. There are literally millions of stories on the site covering fandoms in books, movies, tv, comics, plays, and games. Most specific fandoms also have their own archives. Just use a search engine to search "fanfiction" and your fandom.
A note of caution: Keep in mind that fanfiction rarely goes through and editorial or review process. So some is really very good and some is horrendously bad. In my opinion it's the search for the great story that's half the fun.
Also fun fact: The book Fifty Shades of Grey began life as a Twilight fanfiction.
That's it for today. DFTBA!