To find peer reviewed journal articles in SLUth Search Plus, search for your topic and then use the limiting features on the left side of the page. In the Refine Results section, click on the box that says "Peer Reviewed."
Applying this limiter will update your results and you'll be left with only peer reviewed journal articles.
Most library databases have similar options, although you might find them in a slightly different place, depending on which database you're using.