Most material on the Web has not been subjected to referees or editorial boards to ensure quality. Thus, with respect to Web material, always ask: "Can I trust it?" Anyone can post anything on the web. There is little filtering or refereeing process.
Thus, skilled researchers know they must carefully examine the diverse treatments of their subject, properly interpret research material, and address the frequency with which resources contradict each other.
.edu for educational or research institution
.com for commercial enterprises or organizations
.org for nonprofit organizations
.net for networks
.gov for government agencies
.mil for military bodies