Copyright is a legal concept that grants the creator of an original work exclusive rights to its use and distribution. Technically under US copyright law your self published work is protected as soon as you put the pen to paper. Which means you don’t really have to register it with the copyright office, but it is helpful to do so. Registering your work gives you a little more protection over your material. When you register it through the copyright office, you create a public record of your authorship.
This helps you from pirates, yes pirates, those people who thought your book is awesome and doesn’t want to pay for it and wants to share your awesomeness with the world, or make money from your hard work for themselves. Registering your work protects you. You can send said pirate, or pirate site an email explaining that this book is copyrighted, and they are breaking the law. You give them a warning, and let them know that the next step will be reporting it to the copyright office. There is a hefty fine for copyright infringement.
Copyrighting also helps you protect your work from shady publishers as well. And trust me they are out there preying on the naïve writers who just want to share their books with the world. So whether you register or not that is your choice, but I would rather be safe then sorry.
I suggest that if you do register do it online through their website, it is cheaper that way.
Tomorrow I will talk about places to publish & I am hoping to have another post of just helpful links.