Scholarly articles (sometimes also called academic or peer-reviewed) have some key characteristics which distinguish them from other kinds of sources.
1. Author - scholarly articles will prominently feature the author's academic affiliation
2. Abstract - scholarly articles often feature a summary of the article at the beginning, called an "abstract."
3. Intended Audience - scholarly articles are often written for other scholars in a specific subject (ie. sociology), so you will often find specialized vocabulary or jargon throughout the article.
4. References - scholarly articles always feature lots of references, cited throughout (in parentheses or footnotes), and listed in detail at the end of the article.
5. Charts & Tables (not Ads) - scholarly articles rarely feature images other than graphs and charts, and almost never have flashy ads or graphics.
The term peer-reviewed describes a smaller section of scholarly articles which have been reviewed prior to being published by other scholars in the same field (the 'peers' of the author). Most, but not all, scholarly articles have been peer-reviewed. To find out whether an article has been peer-reviewed, you can check the journal's website - try Googling the name of the journal that the article was published in. Nearly all journals will have the words "peer-reviewed" in their descriptions or on their "About" page.
When looking for articles in the library's databases, you can almost always click a checkbox to limit your search to "peer-reviewed" or "scholarly" articles.