Primary sources are original materials created in or near the time period or event, or by the person or entity, being studied. They are the evidence used to support scholarly work, offering the closest possible view of historical subjects.
News articles, books, diaries, photographs, maps, government documents, photographs, artifacts, genealogical records, advertisements, statistics, and many other source types offer the researcer a first-hand look at historical events, individuals, places, daily life, politics, and much more.
Primary sources are accessible through library databases, a large and growing number of digitized online collections, and the physical collections of libraries, archives, special collections, museums, and historical societies. This guide from the American Library Association is a great overview of finding, evaluating, and even citing primary resources found on the Internet.