Peer review is a process whereby articles are written by experts in a particular field for an audience of other experts. A writer submits his article, and it is reviewed by his peers, other experts in the same field. It is generally considered a higher standard of publication. That doesn't mean that publications peer-reviewed are necessarily bad or inaccurate or that you can't use them for your research. It's just a different standard of publication for a different audience.
If you are looking for peer-reviewed articles on a specific subject we recommend you start with a database dedicated to that subject.
For more information about peer-review check out this library guide, what is a peer review article, or watch this video https://youtu.be/BKhq68F3BwI