If you're looking for articles, start with a list of recommended databases in your area of study.
The term primary source is used broadly to embody all sources that are original. Primary sources provide firsthand information that is closest to the object of study.
A secondary source is a source that provides non-original or secondhand data or information.
References
Galvan, J. L. (2013). Writing literature reviews: A guide for students of the social and behavioral sciences. Glendale, CA: Pyrczak.
Persaud, N. (2010). Primary data source. In N. Salkind (Ed.), Encyclopedia of research design. (pp. 1095-1098). Thousand Oaks, CA: SAGE Publications, Inc.
Secondary Source. (2005). In W. Paul Vogt (Ed.), Dictionary of Statistics & Methodology. (3rd ed., p. 291). Thousand Oaks, CA: SAGE Publications, Inc.
Weidenborner, S., & Caruso, D. (1997). Writing research papers: A guide to the process. New York: St. Martin's Press.