Note: Before Mac OS X Yosemite, the entry for iCloud Drive used to be called “Documents & Data”. Please be aware that if you have enabled iCloud Drive on your iPhone, you must upgrade to Mac OS X Yosemite so that you can activate iCloud Drive on your Mac as well (otherwise your cards won’t upload to iCloud).
Your decks will then show automatically after a few moments.
Note: This particular feature requires either the full version of the app or the purchase of the upgrade to the full version from within the free version.