To limit to scholarly resources in Discovery Search (from the library homepage), choose the "Peer Reviewed" limiter under the "Limit To" filters section, located in the left panel, or under the "Group & Refine This Search" section of the search results (whichever is applicable). In Advanced Search, select "Only return peer-reviewed articles" under "Search Tools."
Peer-reviewed journals have articles that go through a formal peer-review process, though content like letters to the editor (which will still appear in your results when selecting this facet) do not.
Academic journals include peer-reviewed journals, such as the Journal of Structural Engineering, and non-peer-reviewed publications like National Geographic, Discover, and Scientific American.