Well, I want to include.com in your list also because we use it mostly. So .org, .net and .com suffixes are top level domains.
A domain name is the address where a users can access your website.
Experts categorize domains as per purpose.
If you want to open a website for networking purpose then you will use .net platform.
Ex- slideshare.net , www.php.net
If you want to open a website just for not for profit (non-profit) then you will use .org platform.
Ex- www.worldwildlife.org
If you want to do activities for commercial purpose(business etc) then use .com platform.
Ex- www.google.com, www.answeree.com
.org:
This extensions is designed for organisations which can be slight grey area when trying to actually figure out you know what is the definition of an organization but for the purpose of domain extensions it simply means non-profit organisation.
.Net:
The extension stands for Network and it was originally used websites which had multiple sites attached to one website so this just reinforced the fact that they were part of a network of website however now this has changed and the .net extension can be used by anyone specifically before you could only use if you are network and it's common use is quite hard to define now because in my experience .net is used to by computer technology websites.