A primary source is something written during the time period of the event that provides data or a report of original research. For example, when writing about the U.S. Declaration of Independence, the actual Declaration of Independence counts as a primary source. It was written at the time of the event and by people who experienced it. Other examples of primary sources include speeches, official documents, photographs taken at the time, diary entries, interviews, letters, or newspapers printed at the time of the event.
In comparison, a secondary source is something written or created AFTER the event wherein the author did not have firsthand experience of the event. For example, a paper published in the 1900s that analyzes the Declaration of Independence is a secondary source. The declaration was created in 1776, so a paper written over 100 years later would not be a primary source. The author did not experience the event nor was it created in 1776. It is interpreting the event, not providing raw source material like the original document that is the U.S. Declaration of Independence does. Other examples of secondary sources are history textbooks, encyclopedias, reviews, and biographies.
Note to remember:
Primary = comes first; firsthand account of the event(s) at the time of the event(s)
Secondary = comes after, recounting the event(s) by someone not present or long after the event(s)