Copyright applies to all work. The author/creator holds all the rights associated with that work,* and anyone who wants to use that work must ask for permission. However, these requests can be difficult and time consuming for both the authors (content creators) and the users (content consumers).
Creative Commons licenses allow authors/creators to easily communicate which rights they are comfortable giving to any potential users of their work.
This guide is based on information from the Creative Commons website. Please refer to the Creative Commons website for more detailed information.
*Unless the author/creator signs their rights over to another party (for example, a publisher). In this case, anyone who wanted to use the work would seek permission from the publisher (the copyright owner) rather than the author/creator.