It is not always possible or appropriate to use OER. There are other choices that are also more affordable for students.
These materials are not necessarily openly licensed, and as such, have restrictions on downloading, sharing, changing, etc.
When in doubt about how you can use a material, know that it is always safe to link out to the resource. This is true of library-provided articles and books.
Do you have questions about copyright and fair use in an educational setting?
Explore the resources on this guide.