I've read about this book online, and it seems to me like it's some kind of workbook for students. It's a workbook for building vocabulary, as far as I can tell; There's words for students to define, and they can look up the actual definitons. At the end of each section there's SAT, ACT, GED, and SSAT drills and quizzes, and you will supposedly also learn synonyms, Latin words and memorization tools throughout the workbook. (I'm saying supposedly, just to be on the safe side, since I personally hasn't seen or read the book) The words, task and quizzes are Twilight related. You can read about Defining Twilight on
link and read a sample on
link.
I hope this helped :)