If you mean you want to post the actual fanfic here: this is probably not the best place for fanfics; try fanfiction.net, perhaps?
If you mean you want to post the fanfic somewhere else: what do the instructions somewhere-else say?
If you mean the fanfic is already posted but you want to post a link to it here: easiest is probably to put a comment in the current media thread (called “March 2017 Media Thread”). To make a link, write something like this: [what you want displayed](url for link).
If you mean you want to post the actual fanfic here: this is probably not the best place for fanfics; try fanfiction.net, perhaps?
If you mean you want to post the fanfic somewhere else: what do the instructions somewhere-else say?
If you mean the fanfic is already posted but you want to post a link to it here: easiest is probably to put a comment in the current media thread (called “March 2017 Media Thread”). To make a link, write something like this: [what you want displayed](url for link).
Thank you.