Easiest thing is to go to the "Stories" area and read a few. See what stories you enjoy the most, which stories stimulate your fantasies. Then put your own fantasies down on paper, nothing terribly long, perhaps ten pages or so. Let your story sit for a week or so, then buff it up and send it in to the "Submit Story" area!

Perhaps as an intermediate step try reviewing a few of the posted stories.

Good Luck