1. Click on the Apple icon in the top left of the menu bar
2. Select the menu “System Preferences…”
3. Once the System Preferences open, click on the “iCloud” entry
4. Enter your iCloud account information
5. Confirm that “iCloud Drive” is checked (starting with Mac OS X Yosemite)
6. Now you can move some of your decks into the folder “Flashcard Hero” in iCloud Drive

If iCloud Drive is activated on at least one of your devices, all other devices must also use iCloud Drive (instead of “Documents & Data”). iCloud Drive was introduced with iOS 8 and Mac OS X 10.10 Yosemite.

It can take a few moments for decks in the folder “iCloud Drive → Flashcard Hero” to appear in the iPhone app after you have first moved them to iCloud.