Good spellers are encoders—good readers are decoders. While most good encoders are also good decoders, the reverse is not always true. Many good readers simply can't spell because they don't have a solid grasp of the rules behind the often erratic spelling of English words. They can identify words when they see them but can't recall how to spell them when composing their own material.
The Handy English Encoder Decoder won't provide a crash-course in phonics or simply tell you how to spell the word you're looking for. It will help you identify the rules governing spelling and usage so you can encode words yourself and know how to spell similar words in the future. This little volume is a reference designed kind of like an English/foreign language dictionary—the first half ("Encoder") contains phonics rules organized by type, while the second half ("Decoder") contains the same rules in alphabetical order by spelling.
With more than 200 phonics rules, rules for dividing words into syllables, and lists of commonly confused swpellings and word pairs, there's far more to this book than may at first appear. And it's small enough to fit in your inside coat pocket (making it easy to impress people when you produce it with a fluorish and flip to the correct page). An appendix contains three games to help further internalize rules (the letter chain game makes a great party diversion) and an exhaustive list of English homophones (words with the same pronunciation but different spellings).
This book, if used whenever a difficulty is encountered, will certainly make you a better speller and a better reader. It's small and easy to use, and covers just about every difficulty you'll encounter. Not a course in itself, the Handy English Encoder Decoder is nevertheless an excellent supplement to any phonics, reading or spelling course, as well as a great tool for older students and even adults who still struggle with proper spelling.