Many library databases will offer a filter to limit your searches to peer-reviewed or academic articles. These are also known as scholarly articles. However, there are other indicators. 

Scholarly articles will often include: 

• The article title and publication title that will be specific to the discipline and topic
• An abstract (short overview of the article)
• An introduction that describes the topic or problem and the author/s thesis
• A main body of the article that may include a literature review, a discussion, a method and result section
• Charts and/or graphs if the authors conducted research and need display their findings
• A conclusion which summarizes the author's argument, experiment, or study
• A list of references at the end of the article citing previous scholars

Librarians at NCSU have created an Anatomy of a Scholarly Article tutorial you can explore to learn more and their video tutorial, Anatomy of a Scholarly Article contrasts a popular and scholarly article.

If you are unsure whether or not a publication is peer-reviewed, you can search for the name of the journal on the internet and look for information provided to authors. For example, here is Nature's Editorial Criteria and Processes which describes the peer-review process they use.

* Peer-reviewed journals may include non-peer-reviewed content— book reviews, letters to the editor, essays, or editorials.