New York City, draft riots, 1863, from Harper's Weekly.
A few lines in a memoir, a snatch of recorded conversation, a letter fortuitously preserved, an event noted in a diary: all become luminous with significance--even though these are just the bits that have floated to the surface.
Edmund Wilson, To the Finland Station; Forward
Scholars sometimes talk about primary and secondary sources, and for your assignments your professor may require you to consult and cite both kinds of sources.
Primary sources include firsthand, or original records, objects and evidence from the time period you are researching.
The secondary aspect of sources comes into play when there is interpretation, analysis, restatement of these same events or materials in order to explain them.