Application uses in background Leitner System which is the best method for memorize anything.
Flashcards are sorted into groups according to how well the learner knows each one.
You try to recall the answer written on a flashcard. If you succeed, then card is promoted to the next group. If you fail, card is demoted to the first group
The advantage of this method is that you can focus on the most difficult flashcards, which remain in the first Boxes.
The result is, ideally, a reduction in the amount of study time needed.