katakana radicals in in kanji
I am starting to learn kanji, and I'm memorising the radicals so I can use them as mnemonics later to make it easier. I understand that some radicals can't be used as kanji on their own. How do I find out when these radicals are used? And what they mean? Also there are katakana characters such as 'yu' 'to' 'ma' that are used as radicals in some kanji. Is there a reason for this? Do they mean anything?
Many thanks in advance!

Question

Answer

Can you open these links?
All Japanese chalacters are born from Kanji about 1000 years ago.

https://commons.m.wikimedia.org/wiki/File:Katakana_origine.svg

http://www.planeta.rs/21/5temabroja.htm

Answer

You must memorize when to use each radical, there isn't really any secret trick to know when to use each radical or reason why it's there.

I see a lot of resources try to tell people that kanji look like what they represent or radicals have meaning, but they really don't. The radicals in a kanji don't really don't "mean" anything, the radicals in the kanji are there just because. Unless the radical is by itself, it don't mean anything. It's just how the word is written. Many kanji have are archaic origins or look like what they represent, but this doesn't help with memorizing kanji very much.

For example, this is the kanji for the color purple: 紫. It has the radicals: 止(to stop) 匕(katakana hi) 小(small) 幺(short thread radical) 糸(thread.) What do the radicals mean in the kanji and have to do with "purple"? Nothing. Many radicals have no meaning at all, just names people give it.