The "Create Peer" button makes a new card with the same parent (if any) as the current card. The Parent Name, Child Stack Name, Parent ID, and Parent Stack Name are taken from the current card and set up on the new Peer Card.
The Parent Card of the new Peer Card is told about its new child as the new card's ID is added to the end of the Parent Card's "Child IDs" field.
The cursor is placed in the "Self Name" field to encourage immediate naming by the user.
Cards don't need to have names ("Self Name"). It just makes the database easier to use if they do. HyperArchy does not screen for duplicate peer names, nor is it sensitive to duplicate names.