The difference between Katakana and Kanji is fairly easy when you get the hang of the written language! Katakana is basically used to translate English words in to japanese. There are several English words used in Japan, for example: ベッド (beddo) - means bed. Kanji is much more intricate (most of the time) there are however some simple kanji. there are some pretty good descriptions on kanji that I'm sure I wouldn't do any justice. Anyways, hope I helped! :)

Hola, la respuesta de Arianna es correcta. Si eres principiante, no tienes que preocuparte por kanji, aprende hiragana primero, luego katakana, no tienes que usar kanji que no sabes su significado. Sabrás kanji poquito a poquito después de comenzar a practicar japonés con las frases fáciles y simples. En ese momento, ya distinguirás que se use kanji o katakana para una palabra. ¡Mucha suerte!