Domain suffixes help you evaluate a website.
.edu - educational institution / Caution - Can be student originated material if it has tilda ~
.mil - military
.net - network, a variety of sites have this domain
.org - traditionally a non-profit organization
.com - commercial site, usually with the purpose to persuade or sell
Suffixes can also denote geographic origin .au - Australia
If in doubt as to the owner of a domain name, you can search the site on http://whois.domaintools.com/
This site provides information about the owners of registered domain names.