Under US copyright law (Title 17 of the US Code) and the Berne Convention, copyright in an original work exists from the moment the work is fixed in a tangible form — the moment you save your manuscript. No registration, no notice, no symbol is required for copyright to exist and be enforceable.
This means: your book is already protected. Someone who reproduces substantial portions of your work without permission is already infringing your copyright, regardless of whether you have registered or displayed a copyright notice.
Registering your copyright with the US Copyright Office (copyright.gov, cost: $45 to $65 online) creates a public record of ownership and, critically, enables you to sue for statutory damages and attorney's fees in infringement cases. Without registration, you can still sue for actual damages but these are often difficult to quantify and may not exceed the cost of litigation.
For most authors, the practical recommendation is: register before publication or within three months of publication. The fee is minimal and the additional legal protection is meaningful if infringement ever occurs.
Every published book should contain a copyright page (typically the second or third page of the book) stating: the copyright symbol, the author's name, the year of publication, all rights reserved, and optionally the ISBN and a disclaimer for fiction. This page is not required for copyright to exist but it is the professional standard and it serves as immediate notice to any reader that the work is protected.
We include a correctly formatted copyright page in every book we publish as part of the standard interior formatting service.