You can read the book's
introductory essay on the subject, or, if you're feeling adventurous, read David Foster Wallace's Authority and American Usage, an essay / review of the first edition of Garner's book.
Choosing history
essay topic, finding reliable sources, making a research at the
subject, analyzing, brainstorming, creating the
introductory part, writing the body, thinking about the conclusion, inventing the argumentative thesis, and all the other boring activities are waiting for you if you have decided to write your history
essay on your own.