Do I need to register my thesis for copyright protection?
Copyright of your thesis is secured automatically when the thesis is created, and it is "created" when it is fixed in a copy for the first time. However if you'd like, you may register your copyright with the U.S. Copyright Office.
Why should I register my work if copyright protection is automatic?
Registration is recommended for a number of reasons. Many choose to register their works because they wish to have the facts of their copyright on the public record and have a certificate of registration. Registered works may be eligible for statutory damages and attorney's fees in successful litigation. Finally, if registration occurs within 5 years of publication, it is considered prima facie evidence in a court of law. See Circular 1,Copyright Basics, section "Copyright Registration" on copyright.gov.
The library recommends applying a Creative Commons license to your work. What is Creative Commons? Creative Commons is a nonprofit organization that enables the sharing and use of creativity and knowledge through free legal tools. Their free, easy-to-use copyright licenses provide a simple, standardized way to give the public permission to share and use your creative work -- on conditions of your choice. CC licenses let you easily change your copyright terms from the default of "all rights reserved" to "some rights reserved".
Creative Commons licenses are not an alternative to copyright. They work alongside copyright and enable you to modify your copyright terms to best suit your needs.