romanji, kanji and so on
Foxygal: Katakana and Hiragana are NOT an alphabet per se but a way of writing down the sounds of the language and once you learn these you can be able to read what is written on top of/in parenthesis next to the Kanji (Chinese characters) in texts. I would HIGHLY recommend that you learn those first so that way you don't use "Romaji" as a crutch and thus hindering your progress in being able to read Japanese. It also comes in handy if you "forget" how to write a certain Chinese character, then you can fall back on Katakana and Hiragana. Kana is just a word to refer to Hiragana and Katakana, Furigana is the small printed Hiragana and/or Katakana written on top of the Kanji.
When I type in Japanese, I hit a button called "Kana" and when I type I make sure that I am able to convert the word "tegami (letter)" to "てがみ(Hiragana)テガミ(Katakana)" or in Kanji as "手紙" when I type it. It should give you a drop down option that allows you choose which one you want. Otherwise it will just type out random ones that don't have anything to do with the sound that it corresponds with on your keyboard. AIUEO and N are the only sounds in Japanese that can written without another vowel accompanying them. "tegami" would be 3 written sounds: て・が・み／テ・ガ・ミ (te-ga-mi).
Hopefully this helps and makes a bit more sense.
lovelanguagesII: Katakana can also be used to add emphasis to a word, company names, onomatopoeia, as well as plant and animal names too. Hiragana and Katakana are not too difficult to master once you get the used to which character makes which sound and which ones have exceptions. Then there's of course Chinese characters that have a completely different meaning altogether in Japanese too.
The easy way is to buy a textbook which spells everything out phonetically in our Latin alphabet.
There are two problems with this:
a) That's not how Japanese people write so it will teach nothing about reading real Japanese.
b) you looZ a lot of context chewal inform Asian that way. itz laik reedin inglish laik this its reel lea confUsing bee caws ortho it givz U an eye deer of how the wordz sownd owt loud yoo hav 2 thingk kwait hard a bow t what yoo R reed ing. two mennee hommonimz ewe sea.
I recommend spending a week working to learn hiragana. Then you can use a furiganising program to give you the readings of kanji you don't know yet.
>> which means even more confusion because now there is 'kana' 'romanji' 'hiragana' 'kanji' 'furigana'
In fact there are only three scripts:
Hiragana and katakana are called 'kana'.
romaji is not official script
furigana is small hiragana above kanji that helps learners to read kanji.
Ahh this proves more difficult than I thought, generally I see these syllabaires being used - てえつちふへほ which is called 'kana' on my keyboard, which means even more confusion because now there is 'kana' 'romanji' 'hiragana' 'kanji' 'furigana'
so many different ways of writing! I am not sure which one i'm supposed to be learning i'm finding it hard enough as it is to learn the speaking :(
I'm not a native speaker myself and there are certainly more advanced learners of Japanese around here, but I'll try to answer your question nevertheless.
As for the usage of the three writing systems, I'm afraid you'll have to know all three of them because all of them are commonly and routinely used in any type of Japanese text. Our alphabet is totally different from hiragana and katakana because they are no alphabets but syllabaries. I find the writing system in Japanese even more complicated than the Chinese one. One of the major challenges are the different readings of kanji (on-reading and kun-reading, the first being the one "borrowed" from Chinese and the second being the Japanese reading of a character; to make things worse you will encounter lots of characters that have several on-readings and several kun-readings).
Katakana is mostly used for loan words from other languages (such as English) and to highlight words in a text (when we normally would use italics or bold letters). Hiragana, as far as I know, was originally used by women only before it was also adopted by men. There are several historical reasons for that. You will also find "furigana". These are hiragana written above or next to kanji which are not part of the jouyou kanji (the most common kanji taught at school) so that people who only studied the jouyou kanji are able to read them.
All in all, the Japanese writing system is very, very challenging - at least in my opinion. I understand more than I can read, i. e. I sometimes understand the meaning of a kanji but have no idea how to read it properly.