Creative Commons provides a set of basic licenses that dictate how others can and cannot use your work. The most liberal of these licenses (CC-BY) tells others that they can use your work however they like as long as they give you credit. In contrast, the most conservative license (CC-BY-NC-ND) indicates that your work cannot be adapted and cannot be used for commercial purposes.
Creative Commons licensing help chart from Foter.(CC BY-SA 3.
Additional information about different types of CC licenses from the About the Licenses page of Creative Commons.