On and Kun Readings of Kanji

Kanji's readings are separated into two categories, On (un) and Kun (kun). On means the original Chinese reading. All kanji have Chinese readings becuase kanji formed in China and then the Japanese borrowed them and stuck on Japanese readings. Kun means the converted Japanese reading. Most kanji have multiple readings and these multiple readings are very difficult to learn. Also, when you add two or more kanji together their meaning might change or expand making the concept different.