What are primary sources?
Primary sources are original works created by a person who witnessed or participated in an event. Examples include diaries, memoirs, letters, newspaper and magazine articles, photographs, and manuscripts. Government materials are sometimes considered primary sources, too.
Secondary sources discuss information originally presented elsewhere. They include scholarly journal articles, books, conference proceedings, dissertations, and class lectures.
Generally, first-hand accounts of an event are considered primary sources and materials created by a person analyzing that event at a later time are considered secondary sources.
Where you'll find primary and secondary sources varies depending on the topic you're researching, but How do I find primary sources? can help you get started.