When do you know when to use Hirogana, Katakana, Kanji?

Hi, sorry to bother everybody again, its one of my quick questions. There's 3 languages in Japanese. But when do you know when to write them?

Watashi is written in 2 ways.......
‚킽‚µ
Ž„

When do we know when to do which one? Sorry if this was posted b4, but i couldnt search for it.

As far as katakana, you can ule that out b/c it is used ONLY phonetically when a foreign word migrates to japan. As far as kanji and hiragana usage, it is taught in schools and as far as i know, you have to see/read enough to know when to use the proper usage.

pls refer to this post, it will help you ALOT and clear you thoughts on which to use:

http://jdorama.com/viewtopic_2562.htm

perhaps you can try the excercise in there, too~

katakana is used for words that are foreign to the japanese language....it is also used in the same way that "italics" are used in the english language....