The library’s resources are specifically designed to provide you access to some of the most reliable sources out there. But that doesn’t mean everything you come across is peer-reviewed! Always make sure to check out the source–if it’s from a newspaper or a magazine, then it’s definitely not scholarly or peer-reviewed! But if it’s from a journal, has an expert author(s) and contains footnotes or works cited, then there’s a good bet it’s scholarly! A handy short cut in the library databases is to limit your searches to only peer-reviewed results, then it’s basically guaranteed!
If you’re ever in doubt, you can always ask a librarian or your instructor!