Background:
At a basic level, copyright registration is a legal formality intended to make a public record of the basic facts of a particular copyright (not entirely unlike filing a UCC-1 to secure your rights in collateral). While registration is not a condition of copyright protection, it makes sense for several reasons, including but not limited to: (i) establishing a public record of the copyright claim; (ii) fulfilling a predicate for filing an infringement claim; and (iii) serves as prima facie evidence of the validity of the copyright and of the facts stated in the certificate (if filed within 5 years of publication)
Registration may be made at any time within the life of the copyright, and for works created since 1978, it is not necessary to make another registration when the work becomes published (though, if published, you may later register the published edition).
Process:
To register an original work, send three things to the library of congress: (i) a properly completed application form (Form PA, available at http://www.copyright.gov/forms/ ); (ii) a nonreturnable deposit (copy) of the work being registered; and (iii) a check or money order for the filing fee (currently $30). Put all three of these together in a single envelope and send to Library of Congress, Copyright Office, 101 Independence Avenue, S.E., Washington, D.C. 20559-6000.
Note that other requirements apply to other media (e.g., if the work is a motion picture, you send in one complete copy of the unpublished or published motion picture and a separate written description of its contents, such as a continuity, press book, or synopsis).
Registration is effective on the date the Copyright Office receives all the required elements in acceptable form, regardless of how long it then takes to process the application and mail the certificate of registration. Unless you send the package CMRRR, you will not receive an acknowledgement of receipt, and likely will hear nothing from them until you get either a certificate of registration indicating that the work has been registered or a letter explaining why it has been rejected.
NB:
While you are no longer required to use a copyright notice, doing so is a better practice because it serves as additional notice that the work is protected by copyright, identifies the copyright owner, and shows the year of first publication. More importantly, in an infringement case, if a proper notice of copyright appears on the published copy, the defendant cannot plead innocent infringement as a defense.
As a practical matter, the notice for visually perceptible copies should contain all the following three elements: (i) the copyright symbol (the letter C in a circle), or the word "Copyright," or the abbreviation "Copr."; (ii) the year of first publication of the work; and (iii) the name of the owner of copyright in the work. For example, Copyright 2005 [your name]. If you put this in the footer, it should be sufficient.