Generally, peer reviewed journal articles are considered to be authoritative, though in some fields information can become dated quickly (e.g. health sciences), so it's important to note the date of publication.
Academic Search Premier and Proquest Central both have a checkbox that you can use to limit results to peer reviewed articles. WorldCat Local (the search box on the library homepage) lets you filter results by format: peer reviewed articles either before or after running your search.
If you already have a particular article and want to check and see if the journal is peer reviewed, you can use the Ulrich's Periodicals Directory to look up the journal. This database and the others mentioned can all be found by going to the Library homepage and selecting the "Articles & Databases" tab.
Regarding articles from non-peer reviewed journals, magazines, newspapers, books, and websites, you can use the CRAAP method - this is a good handout for the CRAAP criteria, written by a librarian at California State University, Chico.