You can use Authoring tools to both adapt and remix an already existing resource, or you can use them to create your very own OER. Some platforms already have authoring tools incorporated into their repositories that can be used for these purposes. Below are some examples.
Adopting OER for your course also opens the door to the world of Open Pedagogy. Students can help contribute to remixing OER for your course or by contributing to other course material for future lessons. The Open Education Group (CC BY 4.0) has a fantastic list of examples of these types of projects with links to the originals.
OER should be evaluated the same way you would evaluate any resource for your course, taking into consideration the content, the ease with which the ideas are presented, and the ability of it to meet your course needs. In addition, when evaluating OER you will also want to consider how it can be presented and accessed by your students. But, the beauty of OER is that you are free to adapt and remix it to meet your needs!
You can find the PDF versions of each below.
As with any resource that isn't yours, be sure to give credit where credit is due! You can use the Open Washington Attribution Builder (CC BY 4.0) to help you select the best attribution for your OER.
Open Washington also has a self-paced workshop available freely on their site here. This workshop will take you through 10 modules, providing a great introduction to OERs.
Finally, two major OER sites, Open Textbook Library and MERLOT, engage in peer review of materials.