A copyright is a form of intellectual property that protects original works of authorship that are fixed in a tangible medium of expression. For example, if you have written a novel that is original (i.e., you didn't copy it from anywhere) and you save it to your computer, you own the copyright to your book. As a writer, understanding what a copyright gives you will help you in determining which licenses to grant regarding your book and how to better manage your writing career.
A copyright gives you the following rights:
The right to reproduce your book.
The right to prepare derivative works (e.g., a film adaptation of your book)
The right to distribute copies of your book to the public by sale or other transfer of ownership (e.g., rental, lease, or lending).
The right to perform your book publicly (e.g., dramatic adaptation of your book)
The right to display your book publicly.
The right to perform the book publicly by means of a digital audio transmission if the book is a sound recording.
Although a copyright gives you these rights, they don't mean anything unless you register your copyright. That's because you can't enforce these rights through litigation without registration.
For more information about intellectual property rights, see https://www.josephperrylaw.com/blog