It is important to understand where in the cycle you are getting the information and the characteristics of each type of resource.
Primary sources present original research by those who carried it out. Examples include research articles in scholarly journals, dissertations, and conference papers. (example)
Secondary sources summarize, reinterpret, reanalyze, or discuss information from primary sources. Examples include review articles in scholarly journals, magazine articles, news articles, and books. (example)
Tertiary sources digest and condense information from primary and secondary sources. Examples include reference works (dictionaries, encyclopedias, handbooks, etc.) and textbooks. (example)