One of the rights reserved for creators is the right to distribute copies to the public by sale or other transfer of ownership, including licensing. Creative Commons licenses allow the creator to reserve some rights, while encouraging participation in the cultural dialog by applying a minimal license that allows copying and redistribution of their work. There are 4 restrictions that a Creative Commons license can require:
The Creative Commons website explains the licenses and what they allow. A creator can also apply a CC0 or Public Domain Mark provided by Creative Commons to signal that they are not reserving any rights to their work, or that there are no known restrictions to the reuse of the work.
Creative commons license spectrum between public domain (top) and all rights reserved (bottom). Left side indicates the use-cases allowed, right side the license components. The dark green area indicates Free Cultural Works compatible licenses, the two green areas compatibility with the Remix culture.
Image by Shaddim, shared under a CC BY 4.0 License via Wikipedia