When somebody creates something, Canadian law automatically grants them full "copyright" over any creative work they make. This means that unless the creators say otherwise, nobody may share their work or make changes to it, except in accordance with fair dealing and other exceptions in the Copyright Act. In order to reuse copyrighted works in ways that don't qualify for these exceptions, permission must be granted by the copyright holder. This granting of permission is referred to as "licensing." Some copyright holders choose to provide a flexible license which allows their work to be reused and shared without advanced negotiations.
Creative Commons is a non-profit organization whose mandate is to make it easier for creators to share their work and/or build upon the works of others consistent with the rules of copyright. They have created copyright licenses that anybody can apply to their work to allow others to share, remix, or use the work without having to seek advance permission. There are different Creative Commons licenses that allow copyright holders to specify the conditions under which their work may be used without permission.
Creative Commons licenses are not an alternative to copyright, but instead exist alongside standard copyright protections. Copyright holders who use a Creative Commons license still hold the full copyright to their work, and can modify the terms of their chosen Creative Commons license to best suit their needs.
This video provides a basic introduction to Creative Commons:
Wanna Work Together by the Creative Commons Organization and licensed under a Creative Commons Attribution (CC BY) license