Prepare for your Kanji proficiency tests with the software or simply learn more about the language itself. See the yomigata of the characters, write it on the DS screen with the stylus and check its meaning through the attached dictionary.
You can adjust the difficulty level and the speed at which you learn. Set it higher if you are cramming for a test and set it lower when your child are learning his first words. Besides Kanji writing, there are trivial tests you can take with the software to broaden your knowledge of the Japanese language.