You do not need to register your copyright or even place a copyright notice on the work to enjoy the protection of the copyright law. Materials are copyrighted as soon as they are created.
It is a good idea to put a copyright notice on your work. A simple statement will let others know that the work is covered by copyright and that YOU hold the rights. The customary form is the word "copyright", the year, and the name of the creator.
Copyright 2001 by Prof. Ima Mentor
You can establish the strongest legal claim by paying a nominal fee and registering your copyrighted materials with the US Copyright Office. Forms for registering copyright may be downloaded from the US Copyright Office website.
The Creative Commons organization offers a variety of licensing options for creators who would like to retain some copyright protection but still allow others to use and build upon their work.