Secondary sources do not report the findings of individual research studies and often take the form of book chapters, review articles, and commentaries. Secondary source may or may not be peer-reviewed and, typically, are not used as evidence to support your research question or hypothesis. However, secondary sources are great resources for introducing you to a topic or describing concepts you are unfamiliar with. Examining the references section of secondary resources can be used as a strategy to find relevant primary sources.
Review publications contain articles that review the research literature already done in a given area. A review article can give you a good up-to-date synthesis of a particular topic and provide you with an extensive bibliography.