Your original creative works or works that you commissioned or purchased for your business are your private property. You have copyright protection when you publish those original creations or when you register them with the United States Copyright Office.
Generally, you will then have control over how other people use your creation. If you discover someone on a video-sharing website using part of your song or a blogger quoting big sections of your original essay, can they defend their use of your creation by claiming fair use?
Only specific actions constitute fair use
Fair use rules for intellectual property exist to encourage more creation and cultural commentary, not to provide someone with an excuse to steal your creation. Typically, there several kinds of use that fall under the fair use category.
Both critical review and parody, as well as teaching, research and news reporting, could all constitute fair use. However, the intent of the use, including whether the other party profits from it, influences whether the courts will agree that their actions constitute fair use.
Completely reprinting a chapter of your book could be a copyright violation, but pulling out individual sentences or paragraphs to criticize or quote them in a book review would not necessarily be a violation. To determine if you are in an actionable position when someone uses your copyrighted work without permission or compensation, you should look at their intent and the overall impact their actions may have on your original work and ability to profit from it.
Reviewing intellectual property rules and registering a copyright are important steps for someone who believes that others have violated their copyright protection.