There are several types of Japanese letters, alphabets. The main letters are 3 types: hiragana, katakana, and kanji. Other than them, romaji, Roman character and Arabic number are used. Each type of the letters is used at different occasions.
Hiragana is used for nouns, particle, and ending of adjective and verb. Hiragana is phonogram and they have their own pronounce. Katakana is used for foreign words, onomatopoeia, and scientific terms. Katakana is also phonogram. Kanji is mainly used for a noun, stem of verb and adjective. Unlike hiragana and katakana, Kanji is ideogram and its letters describe meanings. The number of kanji which is used usually is about 2,000 letters.
Kanji means Chinese character and it was imported from China in the ancient are. Hiragana and katakana were made from kanji. Due to the huge number and the unique function, it is hard to remember letters of kanji even if they are limited to those used commonly. On the other hand, it is convenient to use kanji for understanding a long sentence in a short time. Even now, some kanji can be used to communicate with other Asian people including Chinese people.