After you start your Discovery Search (from the library homepage) you can use the limiters on the left hand side to limit to scholarly resources. Choose the "Peer-reviewed Journals" limiter under the "Availability" filter.
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.