How do flashcards decide what to show me?

Every setup is a deck. Grade each card Again, Hard, Good or Easy and the card is scheduled back: an Again comes back in minutes, an Easy in weeks, stretching further each time you get it right. That's spaced repetition. The point is to show you a card right before you'd forget it, not on a fixed day.

Nothing due?

That's good. Come back tomorrow, or open a specific setup deck to add its cards to your schedule.

A card you know keeps coming back

Grade it Easy, not Good. Good means "I got it, keep checking". Easy means "stop showing me this for a while".

Streaks and the heatmap

Your streak and activity heatmap are on Dashboard → Progress. A day counts if you review at least one card, on the website or in the app; they share one history.

Flashcards are part of Pro. See What's free and what's Pro?