When you're searching for articles, you'll find that many of the library's databases have a feature where you can check a box/option to limit your search results to peer-reviewed articles.
If you already have an article picked out, and you want to determine whether it was peer-reviewed, you should find out what journal the article comes from and look it up in Ulrichsweb Global Serials Directory, which you will find under the letter "u" on our Databases page (linked under Find Books & Articles on the homepage).
If Ulrichs says the article was "Refereed," with a little referee-jersey icon (like this ), then it is peer-reviewed.