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

Scholar articles can usually be described with the following form- 

• The article title and publication title will be very specific about the discipline and topic
• An abstract (short overview of the article)
• An introduction that describes the topic or problem and the author/s thesis
• The main body of the article may include a literature review, a discussion, a method and result section
• If the authors conducted research they will include charts and/or graphs to display their findings
• The conclusion 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 and look for information provided to authors, for example, here is Nature's Editorial Criteria and Processes which makes it clear that they use a peer-review process.

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