Creative Commons (CC) licenses are a set of statements that authors can apply to their work to indicate how others may use it. CC licenses indicate whether you as an author would like your work to be cited, adapted, redistributed, and/or used for commercial purposes. You may wish to select a more or less conservative CC license depending on how you see others building on your work.
Note that, regardless of the CC license that you select, you will retain copyright for your work - unless you explicitly choose to transfer or relinquish these rights.
Creative Commons provides a set of basic licenses that dictate how others can and cannot use your work. Specifically, the licenses indicate whether your work can be used by others for commercial purposes, whether others can create derivatives of your work, and whether others must use the same CC license after adapting 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. Don't forget also that if you want to dedicate your work to the public domain, you can use a CC0 license. This, of course, is your most liberal option for sharing work.