Q. How can I insert a new Index Card in this view?
Answer :To insert a new Card (aka Plot Point or Story Beat) into the Index Card View, simply put the mouse cursor over the card that you want the new card to proceed and Right-Click.

Choose Insert New Card and fill in the text of the new card in the menu that appears.

Q. How can I delete an Index Card?
Answer : To remove or delete a Card (aka Plot Point or Story Beat) in the Index Card View, simply put the mouse cursor over the card that you want to remove and Right-Click.

Choose Delete This Card and says YES at the warning prompt that appears.