This is a good one to get out of the way first!
So, I know that I, when I was a total novice at Japanese, was pretty much "durrr?" when it came to the writing system. So I will try to explain the way all three systems are broken down without causing any heartache. XD
The first thing you will ever learn in a Japanese language class is hiragana. Hiragana is the most basic way of writing out a Japanese word; some groupings of hiragana can be replaced by a single kanji character, and some, like the endings of verbs, will always be written in hiragana, to accommodate different conjugations. Hiragana is also used when a rare kanji character, or a meaning not usually attributed to that character, is used. In that case, the hiragana appears in small print over said character, and is called furigana.
Each hiragana character represents a single-syllable sound: all the vowels are represented individually, and the rest are made up of a consonant and a vowel. (Exceptions to this are chi, shi, tsu, and n.)
I've run into a few people who thought they could jump right into kanji without touching hiragana. To anyone who's ever thought that: please, for the love of your sanity, don't! Hiragana is essential to know in order to be able to read kanji.
You can find a comprehensive hiragana chart here. I've also put it in the intro.
Katakana is a form of writing used specifically for foreign names and loan words. Essentially? This is how you write in Engrish.
The Japanese use quite a few English words when they speak and write, and you use katakana for that purpose. Katakana, like hiragana, is syllabic. Say that, instead of the Japanese word for "class" ("jugyou," by the way), you just wanted to write "class." You would sound it out like so: "ku-ra-su." So you'd write the katakana for ku, ra, and su. Katakana is most often used when talking about food, non-Japanese names, and foreign countries. It is also ridiculously fun to sound out.
A creative (and creepy) use for katakana I noticed after learning it was its place in horror manga. Katakana is much more angular and sharp than hiragana or kanji, and, since it purely represents a sound, it has a certain primal quality. In the manga D.Gray-man, all of the Millennium Earl's dialogue ends with a katakana character. And in an episode of Ghost Hunt, when something writes "Shinitakunai" ("I don't want to die") on a piece of paper, the word is in katakana.
There's a katakana chart here, and both charts are in the intro.
And last is kanji. Don't worry about kanji right now, seriously. In my class, we learned hiragana and katakana first, and then learned quite a few sentence structures and verb forms before ever touching a kanji character, and for a new student, I'd recommend the same thing. It really helps put the character in context.
Kanji was pretty much borrowed wholesale from China, so if you write Chinese, you have a natural headstart on everyone else. Unfortunately, kanji can be read several ways. The original Chinese reading can be used, but so can Japanese readings. Most kanji can be read two or more ways, depending on the contest in which it is used. For example, when talking about a non-specific mountain, the "mountain" character would be read as "yama." But if you were talking about Mt. Fuji, you would read the character as "Fujisan."
But really. Don't even worry about kanji until you know hiragana, and are used to using it.
Questions? Comments? "UR DOING IT WRONG"s?
