There are twenty sections of about twenty five pages, each covering a few topics such as "Personality and Human Behaviour" or "Education". About half of each section is taken up by word lists and half by exercises, both graded into three levels. The word lists are based on word frequency and importance in German, so "der Loden" is included in the Level 1 list for "Materials and Textures" even though the English word "loden" is relatively obscure. And the lists cover not just words, but useful phrases like "stecken die Nase in ein Buch".
The exercises are varied and interesting. They involve matching synonyms or antonyms, identifying words that don't belong, completing sentences, picking out "false friends", classifying words into semantic clusters, and so forth, along with occasional crosswords and suchlike. These are supplemented by short passages from actual texts, mostly newspaper articles, for translation. Access to, and the ability to use, a good quality dictionary is assumed.
No number is given, but there must be around 15,000 entries in total in the lists in Using German Vocabulary, with perhaps 12,000 headwords, so even the Level 1 lists would include around 4,000 words. The level 2 and level 3 material will only really be useful for university undergraduates who are going to be tested on the extent of their vocabulary, or perhaps those needing rapid acquisition of vocabulary in a particular domain. It may be true, as the studies Fagan cites in her introduction suggest, that it is more effective to learn vocabulary through a structured approach, but unless vocabulary acquisition is a goal in itself it will be more practical for most people to pick up relatively uncommon words as they arise, in reading or conversation.
This is not a book for beginners, in any event, but the Level 1 lists and exercises could be used by advanced school students or learners at a similar level. I ended up working through those, along with the higher level material in a few chapters. Using German Vocabulary is also considerably more expensive than some alternative German vocabulary books, so I think there is a case for publishing just the level 1 material as a slimmer, cheaper volume aimed at a broader market.