Kun’yomi (くん reading) are native Japanese words that have been associated and attached to kanji as it was being imported.
くんよみ is the original native Japanese pronunciation of a word that has gotten itself a kanji.
In order to make kanji accessible to people who didn’t speak Chinese, hiragana got attached to kanji.
For Example:
This is the kanji for “eat” or “food.”
The on’yomi is しょく.
This on’yomi isn’t usually used on its own to say the word for “eat” or “food.” You often have to combine kanji together to form jukugo in order to create a word using the on’yomi pronunciations.
For example, 夕食（ゆうしょく）means dinner. The kanji are combined to create a word.
The kun’yomi is different. This is the Japanese pronunciation of a word or concept. They applied their word for “to eat” to this kanji.
The word for “to eat” in Japanese is たべます.
This is too long to stick into one kanji. Also, when the kanji is on its own like that, you already pronounce it しょく.
By adding hiragana to a kanji, it shows how to read the kanji.
たべます when written in Japanese and kanji, looks like this:
The period in た.べます shows where the kanji ends and where the hiragana starts (this is for demonstration purposes).
Kun’yomi is basically vocabulary.
食べます shouldn’t be thought of as “the kun’yomi for 食.