You can use CC-licensed materials as long as you follow the license conditions. One condition of all CC licenses is attribution. Here are some good (and not so good) examples of attribution.

Creative Commons licenses give everyone from individual creators to large institutions a standardized way to grant the public permission to use their creative work under copyright law. The six types of licenses are explained.

This webinar will provide an overview of the various Creative Commons licenses, how content with different licenses can be combined, and how to give proper attributions.

This is a tool to help you build attributions.

The ASCCC OERI has developed two self-paced OER courses. At the end of OER Basics successful participants will be able to:
1) Properly identify the creative commons (CC) license on a resource and describe how this resource can and cannot be used.
2) Discuss the advantages and disadvantages of open resources using current research in the field as evidence.
3) Research, analyze and review repositories of open resources.
4) Effectively search for open resources and post reviews in an OER repository.
5) Create an open resource by remixing multiple existing resources and designate a license to this new resource based on the licenses of multiple resources used.
Accessibility Basics provides an overview of accessibility not limited the context of OER.