When considering a source, ask yourself some basic questions:
The terms scholarly, peer-reviewed, and academic can all be used to mean the same thing - researched articles where a panel of peer scholars thoroughly examine the article before it gets published. It's not guaranteed to be perfect, but this is the "gold standard" of article publishing.
You can use the CMU Libraries' Catalog or any of our databases to find articles. In the Libraries' Catalog, you can find both books, journals, and some articles, as well. You can also always ask a librarian for help.
Don't forget - you can always use a source you have to find more sources. Use their list of references or works cited!
Most library databases have a "peer-reviewed" or "scholarly" filter in your search. Even the Carnegie Mellon University Libraries Catalog has a peer-reviewed journals search option. Books are a little different - we look for publisher (generally, a "university press") to find out if a book is scholarly. Remember, you can always ask a librarian if you're unsure!
CMU Libraries Catalog
EBSCO Database Search
ProQuest Database Search