Now, in Japanese, we use Hiragana and kanji. However, katakana is important, too. It's used for everything that comes from overseas, the foreigners' names, the names of the foreign countries, the words from other languages...and it's also used for onomatopoeia and other things.So, we need hiragana, katakana and kanji. I hope this was helpful.

The difference is similar to the difference between uppercase and lowercase, or between an upright font and italics. Basically, Katakana are used to emphasize something or for foreign words (think uppercase or italics). Hiragana are used for everything else (think lowercase).

katakana is for load words