Open New Deck
You can use this menu item to open a new instance of a Deck Form set to the same deck as the menu item was activated on (in this case it would be a new instance of the Traditional Tarot. The new deck form behaves in the same way as the principal deck but has a reduced set of menu options. This is referred to as a secondary deck.
Once you have the new deck form you can set it to any other deck by using its own My Decks menu.
Tip: You can also launch a secondary deck set to any deck in your collection by shift-clicking (holding down the shift key while left clicking with your mouse) on that deck in your My Decks menu.