Should I Register for Copyright?
As noted in the Copy(right)s: The Basics section, registering for copyright is not necessary in order to have copyright protection over your works - copyright is immediate for original works in a fixed, tangible form. There are, however, some benefits to formally registering for copyright, and these should be taken into consideration when deciding whether or not to formally register your copyright.
Benefits of Formally Registering for Copyright
Formally registering for copyright mostly gives you more legal protection should you need to bring suit against an infringer. Here are the general benefits to formally registering for copyright:
For more information on the benefits of registering for copyright, see the "Copyright Registration" section (p.5) of Circular 1, Copyright Basics.
How to Register
If formal registration of copyright seems best for your work, go to the US Copyright Office's Registration Portal and choose the type of work you want to register for copyright. You can either register for copyright online (processing time 6-10 months) or using a paper form (processing time 10-15 months).
You will be required to submit two copies of your work in order to be registered. The copy must be the "best edition" of the work you wish to copyright and will not be returned. See Circular 7d for more information on mandatory deposit.
For some unpublished works being prepared for commercial distribution, you can preregister for copyright. Preregistration does not substitute for registration and does not carry many of the same benefits of full registration, such as providing prima facie evidence; preregistration simply acts as a placeholder indicating an intent to register. If you have preregistered your work and become aware of a copyright violation, you must register for copyright within one month of becoming aware of the infringement. See Preregistration FAQ for more information.
For any other questions, see copyright.gov's FAQ for registering a work.
For more information on registering a work, see the US Copyright Office's "Registering a Work" page.