Some assignments require "peer reviewed" articles to insure authority of authorship and accuracy of information.
You can limit your database search results to peer reviewed and full text.
Select "full text" in order to receive the full text of the articles in your search results. Otherwise, you might only get the abstract or summary.
Empirical Research Article - an example of a primary source.
Parts of an empirical research article: Abstract, Introduction and Literature Review, Methods, Results, Discussion or Conclusion, References. Such articles are considered primary sources because they present verifiable data.