Okay so, firt wewe have to write it up on your computer EG: Notebook, Wordpad etc.
Then wewe go log into your profaili (On fanfiction) and go to Publish: 'Upload document' wewe then pakia it and go to new story, pick your characters, rating, title etc and pakia it on there and either preview, hariri au both.
(be sure to hariri it just incase)
It could take awhile to appear on the site but it never takes me long so wewe shoould be alright :D
I think that's how it goes I havn't done it for a little while :)