In the United States, you do not need to take additional action to make sure your work is subject to copyright protections. Once a work has been "fixed in a tangible medium of expression" (i.e., it exists in a tangible, shareable way), it is automatically protected under U.S. copyright law. You are not required to put a copyright notice or symbol on your work, and you do not need to register it with the U.S. Copyright Office. However, there are some benefits to registering a copyright, including the creation of a record of your ownership and eligibility to sue for copyright infringement.

Read more about copyright registration in the U.S. Copyright Office's Circular 1, "Copyright Basics."