To use this app, you must have knowledge of the Japanese phonetic alphabet system, known as Kana. You’ll get to select different sets of alphabets in two different Kana: hiragana (used in combination with Japanese non-kana characters) and katakana (used for writing non-Japanese words in Japanese syllables). 

After selecting your Kana, you’ll be shown Japanese characters one by one, and you’ll have to enter the romaji (romanised pronunciation) for each character displayed. The character turns red when you get it wrong, and green when you get it right. If you’re stuck, you can pull up the alphabet chart by pressing the left button.