Primary sources are original research articles (empirical research), meaning that they are written by the researchers who conducted the research. They are most often written once the research is complete or near completion and are peer-reviewed before being published.
Secondary sources in psychology include articles that summarize or provide interpretations of original research, such as review articles.
The APA Dictionary of Psychology defines empirical as:
"derived from or denoting experimentation or systematic observations as the basis for conclusion or determination, as opposed to speculative, theoretical, or exclusively reason-based approaches."
Look for these clues (i.e. the words) in the title or abstract of the article.
Many original research articles found in peer-reviewed journals follow a similar format and usually include an introduction, methods section, results, discussion/conclusion, and references. Look for all of these elements when you are looking for primary sources.
Secondary sources can be review articles or book chapters.
Review articles are also considered a secondary source.
Secondary sources can often be easier to read.
So, C., & Fiori, K. (2022). Attachment anxiety and loneliness during the first-year of college: Self-esteem and social support as mediators. Personality and Individual Differences, 187, 111405.
Schry, A. R., & White, S. W. (2013). Understanding the relationship between social anxiety and alcohol use in college students: A meta-analysis. Addictive Behaviors, 38(11), 2690-2706.