Index cards are a folder, or substorm, containing other stickies and ideas inside of it. When you delete your index card, you are deleting all of the data inside of it too.
- Click once on the open space in the top bar of the Index Card.
- Click Delete in the pop-up menu to delete the Index Card.
Deleted index cards and the stickies inside of them can be recovered from your trash if there was a mistake.
Also see:
How do I create an index card/substorm?
How do I add stickies to index cards/substorms?