You can think of peer review as a "stamp of approval" from academic experts. When an article is published in a peer-reviewed journal, you can be certain that experts in the relevant field have read it and, independent of their own particular opinions, verified it meets a high standard of scholarship.
Scholars rely on peer review to ensure that the scholarship they exchange with each other is always based in good research and the established standards of their discipline.
The peer review system is similar to quality control systems that you see in everyday life. Just as you might be reassured to see a Health Department certificate in the window of a restaurant, the peer-review system provides an efficient standard of trustworthiness in academic scholarship.
Typically most databases offer a check box to include peer reviewed results only. This box is usually located after the search as a limiter or in the advanced search function.
When conducting a search using the "Search Everything" box on the Kettering University Library webpage, you may limit your results to only peer reviewed sources by clicking where it says "Peer-Review" under "Refine Your Search," in the upper-left corner of the search results page.