"Refereed" (also called "peer-reviewed) means that the articles in the journal are evaluated by a group of experts in the field. These experts must approve the articles before they are allowed to be published. These publications have a much higher level of scholarship and are far more trustworthy than non-refereed journals or magazines.
To help you make sure your articles are from refereed/scholarly journals AS you're searching for them, many databases have limit options. For example:
To confirm that your journal article is from a refereed/peer-reviewed publication AFTER you already have it, check UlrichsWeb for the referee's jersey symbol next to the journal title:
In some journals, particularly those in the sciences, you can look for "submitted/revised/accepted" dates on the first page of the article. These tell you the dates the article went through the various steps of the peer-review process.
Finally, the most authoriative place to look is the journal's website. Just Google the name of the journal. Look for a description of the journal that says "peer-reviewed" there. Also, look at the information for authors or review policy pages. These will often detail the peer-review process for each journal, including which sections of the journal are reviewed and which are merely edited.
Does the source include a bibliography or list of references to support its claims? Are these sources reputable in themselves?
Check for spelling and grammatical errors. If someone hasn't taken care with their grammar and spelling, they may not have been careful about the accuracy of other information included.