In general summery is from 2 to 4 pages long and poitns out main issues of the book, its strengths and weakness. These are also justified, why somethign is strenght and why somethign is a weakness. It also states how worth while the book is to read for different people and in it the category where to book belongs to.
Remember to add source when you justify your arguments and view and have a correcty referencing to the sources.