Primary sources are original records created at the time historical events occurred or well after events in the form of memoirs and oral histories. Primary sources may include letters, manuscripts, diaries, journals, newspapers, speeches, interviews, memoirs, documents produced by government agencies such as Congress, photographs, audio recordings, moving pictures or video recordings, research data, and objects or artifacts such as works of art. Social media posts from services like Instagram and Twitter can also be primary sources. These sources serve as the raw material to interpret the past, and when they are used along with previous interpretations by historians, they provide the resources necessary for historical research.
(From: Primary Sources on the Web. Site includes strategies for reading and evaluating primary sources).
Secondary sources interpret, analyze or summarize. They provide commentary upon, or analysis of, events, ideas, or primary sources. Because they are often written significantly after events by parties not directly involved but who have special expertise, they may provide historical context or critical perspectives. Examples of secondary sources include books, scholarly articles, and (some) news articles.