Full copyright in a work exists from the moment you hit save, put pen to paper, or paintbrush to canvas. That copyright exists for your lifetime plus 70 years. That's a really long time for work to be locked up. Some creators may want total control over their creative works, but others may be interested in having their work built upon by others. Creative Commons (CC) licenses exist to facilitate that reuse.
Copyright is all rights reserved. Creative Commons is some rights reserved.
CC licenses work with traditional copyright to enable easier use of things you create, and allow you to reuse work from others. They do this by communicating, in a standardized way, the rights you want to share with others. Creative Commons licenses replace the individual negotiations for usage rights that traditional all rights reserved copyright requires. If you want to allow others to copy, remix, and share your work, there's a license for that. If you want others to do all of that, but not for commercial purposes, there's a different license for that. See Types of Licenses to learn more.
Creative Commons Explained
Each Creative Commons license has three layers:
A human-readable Commons Deed that is easy for non-lawyers to understand
Machine readable code
Each layer of the license helps a different audience understand what is allowed, and it makes the licenses easy to use.