There are three types of sources:
Primary Sources: are original materials that contain direct evidence, first-hand testimony, or an eyewitness account of a topic or event that you are studying. Please refer to the middle column on this page for more information and examples
Secondary Sources: are scholarly books and articles that use primary resources to solve research problems. For example: a biography on the World Wars, scholarly books and articles.
Tertiary Sources: Encylopedias, indexes, textbooks, and other reference sources that "report" on secondary sources. They provide summaries of or introduction of the topic. Usually they do provide a list (bibliography) or additional primary and secondary sources!
Below are some characteristics that can help you differentiate primary sources from those that are not (ie. secondary):