Once you accomplish "Hiragana", you can write Japanese
Both "Hiragana" and "Katakana" consist of 46 characters each. They are equivalent to phonetic alphabets. Because one character represents one tone the pronunciation can never change, unlike Roman languages.
Once you memorize 46 "Hiragana" characters, you can write and read Japanese sentences in "Hiragana".
We add "Furigana", "Hiragana" or "Katakana" over the "Kanji", for difficult "Kanji", so that you can read the text fully if you have "Furigana" for all the "Kanji" in the text. This is helpful for beginners.