The moment someone creates a work, that item is under copyright and the creator owns the rights to that work. It is up to that author or creator to decide how that work can (or cannot) be used. Individuals who wish to share their original content for educational purposes may opt to use a more flexible license that allows for the sharing of materials. That’s where Creative Commons licenses come in.
Creative Commons licenses “provide a simple, standardized way to give the public permission to share and use your creative work — on conditions of your choice. CC licenses let you easily change your copyright terms from the default of “all rights reserved” to “some rights reserved.” - Creative Commons, About
Creative Commons licenses don't replace copyright, but they work alongside copyright licenses to offer creators more flexibility and the opportunity to share their content.