When you have finished writing a story, you can mark it as “Complete” to let others know that your story has ended. This can help you reach a wider audience, as some users prefer completed stories. 

From Android:

1. Tap on the  Write button in the bottom navigation bar
2. Navigate to the story 
3. Tap on Edit Information
4. Check the button for Completed under Series Status
5. Tap on the  Back button to save