Empirical articles are examples of primary literature.
An empirical article reports the findings of original research done by the authors of the article.
Empirical articles are usually published in peer-reviewed journals.
An empirical article poses a research question or states a hypothesis.
To determine whether or not you've found an empirical article, scan the article (or even just the abstract). Look for an introduction, methods, results, and discussion sections
Review articles in the sciences summarize previously reported findings rather than present new findings, often pulling together the findings of multiple empirical articles. In doing so, review literature often gives a broader view of the current state of understanding in a given topic area.