Whenever you create something, for example; music, a document, or a paper, it is automatically considered copyrighted in the United States. Copyright law gives creators control over their creative work. If people want to use copyrighted work, they have to ask for permission from the creator.
Creative Commons works within copyright law. It allows creators to grant permissions to everyone in the world to use their work by types of licenses. Think of the licenses as overlaying or amending the copyright use.