All of these are domains name: .edu, .gov, .com and .org.
.com , .org , .edu , .gov
top-level domains
commercial websites base their information around selling their product
.com is the domain extension for a commercial website (business, etc.) .edu is the domain extension for Education websites (Universities, Colleges, etc.) .gov is the domain extension for a State or Federal government website. While anyone can get a .com domain. .edu and .gov domains are strictly regulated by ICANN and only official organizations fitting the description of the domain extension can request one.
EDU: EducationGOV: GovernmentCOM: Commercial
To get a backlink from .edu and .gov domains is a difficult task, the easiest way i recommend that you can gain such backlinks is by taking part in projects run by such .edu domains. By projects i mean most .edu domains are owned by Universitys if you some how contribute to projects that they are undertaking you will be able to place a link to your website from your profile page.
Education Commercial Government Network
The ending of a website name has nothing to do with the quality of the information unless it is one of the restricted endings like .gov or .edu. Anyone can purchase a .com, .org, .net, etc.
.Gov tld domains cannot be purchased by ordinary organizations or person - only people from the government are allowed to operate these domains, I'm not sure but i think .gov has more importance in search results over .com such as Google.
I know 5: .com .org .net .gov and .edu
You don't always put a com after it. It stands for commercial. Other common endings include .gov (government), .edu (educational) and .mil (military). Other places end URLs with the company code, like ca (Canada) and jp (Japan).