To find scholarly sources:
The library article databases generally have a checkbox to narrow your results to Scholarly or Peer Reviewed
To evaluate a source's critical reception:
The library's book review databases can show how the source was covered in popular and scholarly press.
To evaluate internet sources:
The internet provides access to all kinds of information, from very scholarly or research-based to popular and entertaining. However, not all information is equally credible or trustworthy. That means that it is up to the reader to evaluate every source that they encounter. There are certain things to check for, such as author, relevance, accuracy, currency and purpose. The About pages on the site can be very useful for evaluation.
Grey Literature refers to "reports, conference proceedings, preprints, working papers, theses, dissertations, personal communications, technical notes" and other ephemeral scientific sources, often published by government, business or academic organizations*. This kind of literature can be key for emerging research and alternative perspectives. To discover the grey literature in your field of interest, browse the article databases for your subject.
Government Publications are a subset of grey literature, and can be important sources for state, federal, and international perspectives on official government proceedings of all kinds.
Tertiary Sources refer to encyclopedias, dictionaries, textbooks and other reference materials that provide broad overviews of particular topics. Where secondary sources summarize and interpret an event or phenomenon, tertiary sources summarize and interpret other resources. They can be a great place to begin studying unfamiliar topics. To find tertiary sources, take a look at the library's collection of online encyclopedias & almanacs, or dictionaries, thesauri, & quotations.
Trade Literature refers to journals, websites, newsletters and other sources aimed at professionals in a particular field. These sources will often report news and trends in the field, reviews of products related to the industry at hand, interviews with leaders in the field, as well as job listings and advertisements. To discover the trade literature in your field of interest, take a look at the library research subject guide for your field of interest.
* Quote from "Grey Literature" in the Encyclopedia of Library and Information Sciences, 3rd Ed.
Information adapted from UC Berkeley Library's Evaluating Resources. Used under CC BY-NC 4.0
A peer reviewed or peer refereed journal or article is one in which a group of widely acknowledged experts in a field reviews the content for scholarly soundness and academic value.
You can limit your search results to peer reviewed materials in many library databases.