You can include any works you have created that you retain the copyright in. You must be willing to place an open license on your work to allow others to freely access and adapt it. See the Creative Commons guide for more information on selecting an open license.
Works that are in the public domain do not have copyright either because their copyright has expired for they are not eligible for copyright. Visit the public domain guide for more information.
Works that have an open license placed on them such as a Creative Commons license can be used as long as your use abides by the license terms. For more information visit the Creative Commons guide.
You may include copyrighted works if you obtain the appropriate permissions or license allowing for distribution for the life of your resource. You must indicate that these resources do not fall under any open license you place on your OER. For more information visit the permissions guide.
For more information on applying fair use to OER see the Code of Best Practices in Fair Use for Open Educational Resources. For more general information on fair use visit the fair use guide.