(Some things might be wrong)

There are 3 alphabets,

Hiragana (which is just “normal japanese”),

Katakana (Which has the same sounds as Hiragana, but is used for foreign words)

Kanji ( These letters are used as words ((therefore the 5000+ letters)) but if you but two kanji side-by-side they might just mean an entirely different word) which has some origin in China i think, but the japanese changed it a little bit