Using a hook in the introduction simply refers to writing a sentence that captures the imagination and attention of the reader. This is usually done with the first sentence as well as your final statement. Using a hook which also sets you up for a common thread throughout the essay is a great way to establish flow. For example, if you're writing about the proliferation of 'everyday celebrity' you can use Andy Warhol's famous quote about 15 minutes of fame for an initial hook and then introduce the rise (and fall) of any flash in the pan celebrity. Throughout the essay you can use the time line of that celebrity's career as a way to advance the story and findings of your paper. This not only makes the paper flow better, it also gives the reader a personal interest to follow.