A peer reviewed journal article is an article that has been reviewed and chosen for publication by the author's professional peers. These peers are scholars in the field, who sit on the editorial board of a journal which is usually published by a professional organization or a university press. Peer reviewed articles can also be known as scholarly or refereed articles.
You have to write a research paper!
Before selecting the sources for your paper, take a moment and review About Journals & Magazines.
Journals document research, and the research is presented using a specific outline: abstract, literature review, methodology, etc. Review the Anatomy of a scholarly article.
Some sources might be based on the author's eyewitness account of an event or an experiment (This would be a primary source), and some of your sources may be an article or book that analyzes a primary source (a secondary source).
When researching in the sciences, here are examples of primary materials:
Secondary sources will analyze research results and/or interpret scientific discoveries.
e.g. Carlson, W. Bernard. 2013. Tesla: inventor of the electrical age.
Research Tip! As a new scholar you will use the sources and materials necessary to answer your research question. If you must select a reference from another discipline, that’s what you do. The examples here are often used by science majors, but not exclusively!