Creative Commons licenses are a great way to help contribute to the open access movement. You are helping to remove some of the traditional cost and access barriers, so that all may benefit.
There are levels of licensing you can choose from. Users are required to give you credit.
How the levels of Creative Commons licenses work.
Almost all OER resources have Creative Commons Licensing. Below is an example from the Open Textbook Library. See the circled area for a CC license.