Historians make distinctions between what they call primary sources and secondary sources. Primary sources are firsthand accounts of events, recorded or produced by witnesses or recorders who were present at the time of the event or experienced the conditions being documented. Primary sources are characterized by their content, regardless of whether they are available in original, microfilm/microfiche, digital format, or published format.
A secondary source is a work that interprets or analyzes an historical event or phenomenon. It is generally at least one-step removed from the event. Examples include scholarly or popular books and articles, reference books, and textbooks.
You can find many primary sources online via the portals below.