A primary source is a document or piece of evidence written or created during the time of study; primary sources offer an eyewitness account of a particular event.
Some examples of primary sources include:
Image source: Wikimedia Commons. Runaway Slave Advertisement. Public Domain.
Links below will provide you with primary sources; they are a very small representation of what's available.
Google is an excellent resource for finding primary source materials. A search of your topic AND "primary sources" will garner additional links.
Additionally, newspaper articles from the time period you're researching may be found in Chronicling America: Historic American Newspapers, Early American Newspapers, the New York Times, or the New York Times Historical. These sources are under the FIND Articles tab.