For katakana and hiragana, it's more like a different strokes for each "alphabet" (example, "あ" and "ア" are pretty much the same "a" sound, just that the former is the hiragana stroke while the latter is katakana. It's pretty much the case with every other sound) and, they're just used for specific words. Katakana is used for foreign words, so for example, the color orange in japanese is "orenji", which is pretty much orange, so it's written in katakana. On the other hand, hiragana is used for actual japanese words. As an example, purple in japanese is "murasaki", which is a word originated from Japan, so it's written in hiragana. Kanji is a bit more complicated in that it's actually chinese character. I still don't get it fully, or really know what the point of it is.