Copyright exists the moment you have created your content. However, that protection is limited unless you register your copyrights with the U.S. Copyright Office. See here for the complete benefits of registering with the Copyright Office.
It is now mandatory to register your copyrights with the U.S. Copyright Office before filing a lawsuit. Only copyright holders who have obtained a decision regarding their application may file a lawsuit. Obtaining a decision from the Copyright Office can take 3-7 months. Pending applications are not eligible.