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.
A work is considered joint if it meets these conditions:
both or all the authors intend that their contributions be merged into a single work;
this intention exists at the time of creation of the work.
No written contract is necessary to create a joint work. Each author owns an undivided portion of the entire work. So, one author can grant another person permission to use the work without the agreement of the author author. The only obligation is to share in any profits received.
Copyright law can be difficult and confusing. This webpage is meant to provide you with guidance, but not legal advice.
Should you have further questions, please do not hesitate to ask Sara Benson, the Copyright Librarian, for assistance. Sara can be reached at 217-333-4200 or firstname.lastname@example.org