~My (hugely simplified) way of remembering it is that the kanji reading is for when the mouth kanji is used as part of another word, usually alongside other kanji. If you want to say the word ‘mouth’ you use the vocab pronunciation.~
Edit: Don’t take this advice it might set you back
The kanji are just building blocks or concepts. They are not words in an of themselves necessarily. This is why the pink kanji lessons can have a different reading to when the kanji is used for an actually word.
Pretty much. くち is the actual word for mouth, but it uses the kanji which, in certain compounds, can also use the reading こう.
Yeah it just takes time and practice but you eventually get the hang of it.
It’s sort of a pain in the neck from the fact that the Chinese writing system (and some Chinese derived readings run through the ears of long ago dead Japanese people) being bolted on top of an existing spoken language that had its own words for many things. So you get this sort of Jekyll-and-Hyde type situation with on and kun readings.
Maybe to get started you could use the analogy of emoji.
= swim (or deep or river, same picture different ways of ‘saying’ it)
ing = swimming (similar to how hirigana letters attach to a kanji and make a word which can have a different meaning than the kanji alone)
= hot, lit, burn ie. Several different ‘pronounciations’
= sunburn (a single word composed of two emojis but only one pronunciation)
Maybe this will help I don’t know, but I’m also a beginner, so some people more experienced may help you better
All kanji have On’yomi and Kun’yomi readings. In general the kun’yomi readings will be used when the kanji represents a vocabulary word, and the on’yomi represents the kanji concept. On’yomi is also usually used in compound words.
The vocab and Kanji readings give you the gist of the different readings in context, so you don’t have to know everything about them other than that there are multiple readings, and that the vocabulary is what you would read if you were seeing that word in a sentence.
my take would be:
Kanji: a picture/symbol representing an idea/concept
Vocabulary: a word (same as words in English)
The kanji 口 is a symbol representing the idea of a mouth/hole/door/whatever else
The word くち is a word meaning “mouth”, and written with the symbol 口
The word じんこう is another word meaning “population” and written with the pair of symbols 人口