Left: word 讠/言 (sound waves out of a mouth 口), right: circumference 周 (A framed 冂 luck 吉, sets its circumference) [joy 吉 = simplification of happy 喜, where the scholar 士 has beans 豆 in his mouth 口 and is happy.]
The app has many other functions, such as character selection according to difficulty, practice programs, handwriting recognition and success statistics!