This is a personalized card based learning system to learn the Japanese characters called Hiragana and Katakana.
It tries to rate each card you answered based on three different filters and applies a "penalty" score for each filter.
The modifier values are then applied to indicate the importance of each filter, you can change them below, the higher the value, the more important that filter becomes. Put all the values together and you get a total "score" for a card. The cards you will get are the ones with the highest score. If cards have the same value, one card is randomly chosen. In the "overview" page you can see your performance as well as the scores each card got assigned.
The filters are all based on your own performance, so the card you took the most time to answer will be considered the maximum score. Even if your slowest is still very fast.
The cards you haven't seen yet usually come first, since there isn't any performance data on them and thus they get the maximum score every time.
The basic kana cards have a hint (the dakuten and doubles do not), a mnemonic to help you remember it. The "Hint timer" is the amount of seconds after which the hint becomes visible.
The "Cards per session" is simply the amount of cards you wish to see in the session you get when hitting "Start".