71 hiragana characters + 71 katakana characters + 2136 kanji characters = 2278 symbols. Why do Japanese need so many of them? Why can't they just have 26, like English? In reality, this kind of writing system, although it can seem quite strange and excessive at first glance, has its benefits that the writing system of English, for example, doesn't have.
By the way, it's not really correct to call all these characters as 'alphabets', let's figure out why that is.
Hiragana consists of 71 letters and is the basis of Japanese writing system. All Japanese children learn hiragana first and your learning process should also begin with learning hiragana.
This writing system might seem quite strange for English speakers, because hiragana is a syllabary. In writing systems of most languages we are usually familiar with, symbols (letters) generally represent some sounds ("a"= [ai], "b" = [b], etc). On the other hand, in writing systems that use syllabaries, one symbol represents a syllable, generally consisting of two speech sounds ("く" = [ku], "る" = [ru], "ま" = [ma]).
Kanji is a system of logographic characters in Japanese. It consists of tens of thousands of symbols but we only need to know 2136 jōyō kanji. The pronunciation of each kanji character can be written down both in hiragana and katakana symbols (more often in hiragana), Japanese children use texts with furigana to learn kanji.
A big advantage of using kanji is that it shrinks texts.
In 2017, Twitter raised the maximum amount of characters per tweet from 140 to 280, at the same time they released an article, where they pointed out that tweets in English on average contained 34 characters, while tweets in Japanese contained only 15.
Very often kanji is combined with hiragana, because hiragana is also used to denote the grammatical structure of a sentence. For example, 食べる ("to eat", is pronounce like "taberu") consists of kanji character 食 (ta) and hiragana characters べる (beru). If we wanted to use this verb in past tense, we would use the same kanji 食 (ta), but a different hiragana 食べた (tabeta) or 食べました (tabemashita).
The majority of people ask themselves a fair question - if we can write down all kanji characters in both hiragana and katakana, maybe we should not even bother learning kanji at all? The problem is that Japanese don't use spaces. Spaces are only used with punctuation. Japanese separate words and parts of sentences by constantly switching between hiragana, katakana and kanji. That's why if you only use hiragana without kanji, your Japanese will looksomethinglikethis. Asyoucanseeitisnotthebestidea. If you use kanji, it will LookMoreLikeThis. ItCanStillLookQuiteStrangeToYou, ButJapaneseGotUsedToIt, ThisIsNotThatDifficult. Only little kids write using hiragana and not kanji in Japan, so, if you choose to write this way, that is who you will be associated with.
Originally, Japanese language didn't have its own writing system, that is why Japanese just borrowed the writing system from China. In fact we can say that kanji are just Chinese logographic characters, although some of them slightly changed. So they had Japanese language and Chinese writing system, the goal is to make them work together somehow. As a result most kanji have two readings (or pronunciations) - original Chinese reading (onyomi) and Japanese (kunyomi). Depending on the context, the same kanji can be read differently. It may seem complicated, but it really isn't as difficult as it looks. Consider, for example, the sentence "This is a very rare record of Chet Baker's 1955 live performance". You have no problem understanding that the word 'record' in it is not the same as in "I want to record our conversation" as well as that the word "live" is not the same as in "I live in New York". If you are fluent in English you have no problem differentiating between these words, so over time you will have less of this problem in Japanese as well.
Katakana is the second syllabary of Japanese. It's characters are pronounced the same as hiragana characters, but they look differently. Hiranaga: く (ku), る (ru), ま (ma) Katakana: ク (ku), ル (ru), マ (ma)
Katakana is mainly used to write down borrowed words.
Most of borrowed words came into Japanese from English. So if you know English and can read katakana, you will automatically understand some words.
Due to the nature of Japanese phonetics some borrowed words may sound strange, but if you want to speak Japanese like a native speaker, you will have to get used to that. Meaning instead of 'computer' you'll have to say 'konpyuutaa'.
Among young Japanese people katakana is also considered a 'cooler' way of writing words. For example, in manga words like "boom", "crack" and "whoosh" will be written in katakana.
Now, when we understand the difference between hiragana, katakana and kanji, let's take a look at some sentences.
ohayou gozaimasu - good morning
Written using only hiragana
genki desu ka - How are you doing?
Consists of kanji 元気 (genki) and hiragana ですか (desu ka)
daijoubu desu ka - Are you ok?
Consists of kanji 大丈夫 (daijoubu) and hiragana ですか (desu ka)
kore wa nan imi desu ka - What does it mean?
Consists of hiragana これは (kore wa), kanji 何意味 (nan imi) and hiragana ですか (desuka)
nihongo de konpyuutaa wa nan desu ka - What does "konpyuutaa" mean in Japanese?
日本語 (kanji) - "Japanese language" で (hiragana, a particle) コンピューター (katakana) - "computer" は (hiragana, a particle) 何 (kanji) - "what does it mean?" です (hiragana) か (hiragana, a particle denoting an interrogative sentence)
jimbo wa ringo o taberu - Jimbo eats an apple
ジンボ (katakana, a non-Japanese name) は (hiragana, a particle) リンゴ (katakana) - "apple" を (hiragana, a particle) 食べる (kanji + hiragana, creating a single word) - "eat"
Patorikku wa biiru ya wain ya arukooru wa nomimasuka - Patrick, do you drink beer, wine or some other alcoholic beverage?
パトリック (katakana, a non-Japanese name) は (hiragana, a particle) ビール (katakana) - "beer" や (hiragana) - "or" ワイン (katakana) - "wine" や (hiragana) - "or" アルコール (katakana) - "alcoholic beverage" は (hiragana, a particle) のみます (hiragana) - "drink" か (hiragana, a particle denoting an interrogative sentence)