How many kana wait in the tray. In Pick mode it's the number of choices (at least 3).
After that many misses on a kana, its romaji appears and its spot glows.
Every kana you miss is saved to your review pile (the Review button). It leaves the pile once you place it right on the first try this many times in a row — in any round.
Handwritten uses a textbook-style font (Klee One, loaded from Google Fonts) that shows strokes the way you'd write them.
Percent placed right on the first try. Grey means not practised yet.
Every kana you miss lands here and stays until you place it right first try 2 times in a row (● = progress).