When editing a story the fourth tab is the Characters tab. This provides the following features:

You can select a Background Type from the Background Type dropdown to see all existing entries, for that background type for the character. 

To add an additional entry for that background type, click the Add Background button when that background type is selected in the Background Type dropdown. To edit or delete a entry for a Background Type, click the Edit button. This allows you to edit the description of the entry and optionally set the Timeline. You can delete the entry by clicking the Delete button.