FanFiction allows you to sort out your stories in communities category by following the below mentioned steps:
Step 1: Tap "Communities" from the tab bar at the bottom of the screen.
Step 2: A list of all the available community categories will appear. Tap on your desired category.
Step 3: A list of all the available titles under this category will appear. Tap on your desired title.
Step 4: All the available stories under this title will appear on the screen. Tap on the story and enjoy reading it.