These are simply first-hand accounts or original records of an event. Primary sources may include newspaper articles, diaries, letters, interviews, maps, government documents, oral histories, videos, illustrations, photographs, and more. A primary source may also be the result(s) of original research, including quantitative or qualitative data.
These are resources that were created “after the fact” by persons who were not present at the actual event–they are simply reporting on information they have received “second hand.” Secondary sources usually offer an analysis or interpretation of primary source materials. For example, most scholarly textbooks and reference sources like encyclopedias would be considered secondary sources.
Whether or not a resource is a primary or a secondary source may also depend on what your topic is and how you are using that resource. For example, a newspaper article written in 1941 about the 2nd World War would be a primary source, but a newspaper article written in 2008 about WWII would be a secondary source. Books that are secondary sources may also contain primary sources within them; for example, excerpts from interviews, copies of government treaties or legislation, or research results. Try to find the original source (looking in the book’s footnotes and/or bibliography will help!) and you can use them as primary sources for your own research topic.
Below are some links to help you find primary sources, but you may also want to check out the Reference and User Services Association’s (RUSA’s) Guide to Primary Sources on the web.