Since you own the copyright to your work (unless you have transferred copyright to another party), CC copyright licenses are a simple, standardized way to give others permission to share and use your work without having to ask permission -- on conditions of your choice.
"Creative Commons is a nonprofit organization that enables the sharing and use of creativity and knowledge through free legal tools. Creative Commons licenses are not an alternative to copyright. They work alongside copyright and enable you to modify your copyright terms to best suit your needs." -- From Creative Commons website