Hiragana and katakana are the two kana syllabaries used to write Japanese. Each symbol stands for a sound unit (a mora) rather than a meaning, unlike the Chinese-derived kanji they are written alongside.
Hiragana, with rounded shapes, is used for native Japanese words, grammatical endings and particles. Katakana, with angular shapes, is mainly used for foreign loanwords, foreign names, sound effects and emphasis. Both sets cover the same basic sounds, with 46 standard characters each.
Source: Wikipedia: Kana