Online Guide for Physics
Evaluating Sources
Whether a Web site or in paper, the same criteria basically apply for both. 
- Author is identified with reliable credentials
- Is the publication itself reliable? a reliable publisher? is the Web page URL coming from a government agency (.gov), an institution or agency (.org, .net), an educational institution (.edu) [.com or personal pages are not unbiased or necessarily reliable]
- Are there references for further reading?
- Do you know where their data comes from?
- How current is the information?
Use the criteria above to decide if the source is credible, accurate and reliable.
If you need to find primary literature, check out those criteria. If all you want is some news about a topic, a newspaper will suffice. It depends on what your need is.