The latest versions of Wiz Solitaire are available exclusively on the Mac App Store. The Deck Editor is not provided, but you can still download it from this address.
In previous versions, the Deck Editor was shipped together with Wiz Solitaire. When you downloaded and mounted the dmg archive, you would have found these files:
Typically, you should drag’n’drop the whole WizSolitaire folder into your Applications directory. In this way you’ll also install the Space deck, which you can use as an alternative to the Standard one (other decks are available for download).