Primary source materials at the NYU Libraries can be found at: NYU Special Collections Center (Bobst Library), Poly Archives and Special Collections (Dibner Library) and the Abu Dhabi Archives and Special Collections
Chapter 6, "The Thrill of Discovery: Primary Sources" in Jenny L. Presnell's The Information-Literate Historian: A Guide to Research for History Students (New York: Oxford University Press, 2007) provides a thorough overview of primary sources. The chapter covers definitions, categories of sources, locating materials, and evaluating sources.