Video from the U.S. Copyright Office describing what copyright involves, including what types of works are subject to copyright protection.
Anything you create is automatically under copyright protection from "the moment it is created and fixed in a tangible form that it is perceptible either directly or with the aid of a machine or device," according to U.S. copyright law. You don't need to register your work or publish it for it to be protected by copyright.
Under U.S. law, a copyright holder has the exclusive rights to do and to authorize any of the following:
Copyrighted material can be used in teaching and research under any of the following conditions: