I just found a great powerpoint presentation made by Professor Charles Darling of Capital Community College. The presentation presents the rules of spelling for American English. Most of the rules are the same as the rules of other Englishes too.
Here's some vocabulary to help you understand. The Japanese translations come from Space ALC. If you want a simple English definition click on the word. Then you can see a definition from Simple English Wikipedia. Also, don't forget to try the Simple English Wiktionary. Ok them, here's the vocabulary:
Vowel - 母音｛ぼいん｝、母音字｛ぼいん じ｝
Consonant - 子音｛しいん｝
Plural - 複数形｛ふくすう けい｝
Proper noun - 固有名詞｛こゆう めいし｝
In order to view the presentation, click the arrow on the player that is pointing right .