Review: The Review tab shows how many cards are due today across all your subjects, split into cards to review and new cards (up to 20 new a day), with a count per subject. Select Start review to begin.
Reviewing: In a review, read the front of the card and try to recall the answer, then select Show answer. Rate how well you knew it: Again, Hard, Good or Easy. Each button shows when you would see the card next. LevelUp uses the FSRS algorithm, so well-known cards come back less often and forgotten ones come back soon. Keyboard: Space to reveal, 1 to 4 to rate.
Offline: On Android and iOS, reviews work without a connection. Reviews are saved on your device and upload automatically when you are back online; if you review the same card on two devices, the most recent review wins.