Primary sources include a variety of materials written or created during the time period of the topic you are researching. They also include things written at a later date by a participant in the events being studied (e.g., memoirs).
Primary sources allow researchers to get as close as possible to a historical event or time period via the viewpoints of actual participants or observers.
The library has full-text online archives of the following American newspapers, which make for great primary historical sources:
There are also many primary source collections available freely on the web. Below are a few general suggestions.