To add a Custom Noun, simply type it into the text box and click 'Add Noun'. The new Noun will appear on the list of custom nouns. You will also be able to use it to create a new story immediately, and any stories that contained the new Noun will attempt to auto-link it from now on.
To delete a Custom Noun, click the red button next to it. The Noun's story (if it existed) will be deleted, and the Noun will no longer be auto-linked by other stories.
You cannot edit an existing noun: you will need to delete and remake it.