The Front Side and Back side content of the Flashcard can be separated by inserting the WordPress ‘more’ tag.
You can find the More Tag button in the first row of the visual editor toolbar or by pressing Alt+Shift+T:
Using the More tag
1) Go to Flashcards -> Add New in your dashboard to create a new Flashcard.
2) Write/Design the Front Side of the Flashcard by putting the content. When finish writing the frontside, insert the More tag to denote that front side content is over. The content after the more tag will be the back side content of the Flashcard.
3) Save the Flashcard.