The Categorical Imperative is supposed to provide a way for us to evaluate moral actions and to make moral judgments. It is not a command to perform specific actions -- it does not say, follow the 10 commandments, or respect your elders.
A blurb on a book can be any combination of quotes from the work, the author, the publisher, reviewers or fans, a summary of the plot, a biography of the author or simply claims about the importance of the work.
A plot summary is a synopsis of a book, play or film's story. For example, this link is for a plot summary of the book Adventures of Huckleberry Finn, and this link is for a plot summary of the film Star Wars (film).