In most fields, scholarly journals do not pay authors, who can, therefore, consent to OA without losing revenue. In this respect, scholars and scientists are very differently situated from most musicians and movie-makers, and controversies about OA to music and movies do not carry over to research literature.
OA is entirely compatible with peer review, and all the major OA initiatives for scientific and scholarly literature insist on its importance. Just as authors of journal articles donate their labor, so do most journal editors and referees participating in peer review.
OA literature is not free to produce, even if it is less expensive to produce than conventionally published literature. The question is not whether scholarly literature can be made costless, but whether there are better ways to pay the bills than by charging readers and creating access barriers. Business models for paying the bills depend on how OA is delivered.
Image by Open Scotland is licensed under CC BY 4.0
OER (Open Educational Resources) are works that have been "opened" by the copyright owner to allow others the ability to "retain, reuse, revise, remix, and redistribute" the work without needing to ask for permission. Credit must be attributed to the creator of the work, and it must have a Creative Commons or other License that removes copyright restrictions.
Open Access materials are available free of charge, but normally are still covered by copyright restrictions.
Image from: https://learninginnovation.ontariotechu.ca/oer/about-oer/rights-and-licenses.php
OERs may be modified to fit the needs of your course. For tips on modifying an open textbook, visit BC Campus and explore the provided links. Another good resource is Modifying an Open Textbook: What You Need to Know by Cheryl Cuillier, Amy Hofer, Annie Johnson, Kathleen Labadorf, Peter Potter, Richard Saunders, and Anita Walz.