I am just a begginer. I finished learning Hiragana . Now , I am learning Katakana . I realized that they are same. So that made me worry a little . How do I decide which one to choose ? Are there any words that you cant use katakana instead of hiragana or hiragana instead of katakana letters in them ? Also, If write it like that will Japanese people can understand what I meant ?
Words of non-Chinese foreign origin are generally written in katakana, for one thing. Besides that, there a few Japanese words it's quite common to write in katakana, such as オシャレ and ダメ. In some works of fiction, a character's dialogue may be written in katakana to project a 'robotic' or 'otherworldly' tone.
Hiragana is used for spelling out Japanese words, and katakana is for words that were adopted from other languages.
While you could write everything with just hiragana and katakana, using kanji makes your text less vague, as with phonetic spelling, your text could be potentially interpreted in many different ways.