Creative Commons offers a number of licences that allow creators of any online content to set certain conditions for sharing and reuse of their work by other people.
When you create an open educational resource that other people can retain, reuse, revise, remix, and redistribute, it doesn't mean you must waive all rights to it and commit your work to the Public Domain - though you can do this if you wish by assigning a CC0 licence to it. A CC BY licence will allow all of the above, whilst still requiring the creator of the retained/reused/revised/remixed/redistributed work to credit you as the original author. Furthermore, a CC BY-SA will not only require them to credit you as the original author, it will also require them to share their retained/reused/revised/remixed/redistributed work under the same conditions - in other words openly.
The graphic below explains the difference between the public domain and the main Creative Commons workspace.