What is a peer-reviewed journal
A journal is refereed or peer reviewed if its articles have been evaluated by experts before publication. The experts advise the journal's editor for or against publication of the articles. Peer review insures that the research described in a journal's articles is sound and of high quality. The process is usually blind; that is, the reviewers do not know the names of the authors and the authors do not know the names of the reviewers.
Keep in mind that a peer reviewed journal may contain material--book reviews, letters, notes, editorials--that has not gone through the peer review process. Also, journal articles which have not been peer reviewed may still be of high quality. It is important to evaluate individual articles for quality and usefulness.
Finding/identifying peer-reviewed articles
Many databases allow you to search specifically for peer-reviewed journal articles. To see if your journal is peer reviewed, try searching Ulrich's Global Serial Directory: a comprehensive database of periodical descriptions, including whether they are refereed. Search for the journal (e.g., by title) and look for the peer-reviewed symbol in the list of results, or for this information on the detailed record.
If Ulrich's does not list the journal, do a web search for the journal title to find a web site for the publisher. Example: Journal of Marketing Research states that it is peer reviewed. If peer review or refereed is not mentioned, check instructions for authors; for example, Human Factors describes their double-blind review option.