Peer Review is a critical part of evaluating information. It is a process that journals use to ensure the articles they publish represent the best scholarship currently available, and articles from peer-reviewed journal are often grounded in empirical research.
When an article is submitted to a peer reviewed journal, the editors send it out to other scholars in the same field (the author's peers) to get their assessment of the quality of the scholarship, its relevance to the field, its appropriateness for the journal, etc. Sometimes, you'll see this referred to as "refereed."
Publications that don't use peer review (like Time, Cosmo, Sports Illustrated) rely on an editor to determine the value of an article. Their goal is mainly to educate or entertain the general public, not to support scholarly research.
Most library databases will have a search feature that allows you to limit your results to peer reviewed or scholarly sources.
Most article databases include an easy way to limit your results to those published in peer-reviewed journals.
In APA PsycInfo and ERIC (and other EBSCOhost databases), there are two ways to place such a filter.