Web address domains are used to categorise websites and can help you identify the type of information you might find on the website.
Common top-level domains are:
.edu (educational) websites that belong to education institutions
.gov (government) belong to government departments and institutions
.com (commercial) belong to private individuals and companies
.net (network) belong to private individuals
.org (organisational) belong to organisations, usually non-profit
Be careful of commercial (.com) and organisation (.org) websites as their credibility is harder to determine.
Always think critically about who the person or organisation is, what information they have made available, what they have not, and why.
Understand how Google works
This video explains how Google search works and how the results are displayed. You might be surprised about your search results!
YouTube video: How search works by Matt Cutts 2010
Google also provide an explanation of their search here