If you wrote an essay or article, you are the owner of that article unless and until you contract away your rights (such as in a publishing agreement).
Giving away the bundle of rights that constitute copyright is often called a grant. If the transfer is exclusive it has to be in writing. In books/articles, this usually occurs in a publishing agreement.
The Creative Commons has developed a series of licenses that allows copyright holders to retain control over their works, but still make them available under terms more favorable than copyright allows. Essentially, under the creative commons licenses, owners of copyright have allowed others to use their work with certain limitations specified in the creative commons license.