Japanese alphabet consists from two types - one is call Hiragana (ひらがな), and the other Katakana (カタカナ). These alphabet are called Go-Ju-On (50 音). However, in this modern age, the actual letters being used are limited to 46 characters.
Hiragana Drill will help to tie the Katakana character to specific sound, and let you practice these 46 letters over and over.