Every kanji is a bento, and every reading is a compartment. Name its readings in rōmaji (they turn into kana) and fill the box.
Tap a kanji to open its bento. Full boxes turn red. Your progress is saved with the rest of your kanji progress, and synced if you use Sync.
Readings come from the same kanji cards as the Wall of Kanji. Which readings count as common, and the example words, come from the real sentences in Kanji in the Wild (Tatoeba, JMdict).