>>741
didn't bother opening your whole post. addendum.
okurigana = just the hiragana used with a kanji's kunyomi reading. when you see hiragana following a kanji that isn't part of a jukugo, then it uses it's kun-yomi.
onyomi = exactly as you said. reading a kanji uses when used in a jukugo.
It even states throughout kanjidamage, there are exceptions to these rules. Some compounds use kunyomi for both kanji, like 埋め合わせ, some use kun-yomi without hiragana, some use a kun/on combination. MOST are on-yomi only jukugo. You just memorize the exceptions as they come. Eventually when you familiarize yourself with kanji enough and know how it "acts" you will come to pick up on when it's an exception case. Because often when it is an exception it's because the on/on configuration sounds weird or awkward.
I want to stress again for you to go back and read the info about what kanji are, how they are made etc because by 242 you should be familiar with how this works. Also take the time to go finish memorizing hiragana before you continue.