Understanding www and non-www domains are very easy. Let’s understand it. When a domain is registered, its name with the registrar is always in non-www form like internetmarketing.technology and it is never www.internetmarketing.technology with the registrar. Then what is www with the domain name? www stands for World-Wide-Web. In fact, this is an automatic and understood sub-domain of your primary domain.
Actually, internetmarketing.technology is your primary domain and but domain like: blog.internetmarketing.technology or forum.internetmarketing.technology are sub-domains. Similarly, www.internetmarketing.technology is actually a kind of sub-domain which is attached with world-wide-web technology on the server, your site is being hosted on. So, this is the main difference between www and non-www domains.
As it had become a trend writing or telling domains names with www in the decades of late 80s and early 90s, so people started hosting their site address with www like www.internetmarketing.technology. Remember, each and every domain name, whether it is primary or sub-domain, is attached with World-Wide-Web on server. So, every domain on the server is also being hosted with www, even your sub-domains also. But it is our duty to redirect them properly either with www only or non-www. A sub-domain name can also be addressed or hosted with www like: www.blog.internetmarketing.technology but generally it is not done. Sub-domains are hosted commonly with non-www addresses and only the primary domain like internetmarketing.technology is addressed with www by default.
It is also clear with SEO techniques. Search engines like Google, Yahoo or Bing etc treat www and non-www as two different domains or directories. If it is not redirected properly, the search engine will consider same site content or duplicate contents and coding with two different domains or directories. So, it is very important to redirect the domain name either www to non-www OR non-www to www to configure it properly with the webmasters tools.
twitter.com is hosted with non-www URLs i.e. twitter.com only
facebook.com is hosted with www URLs i.e. www.facebook.com
google.com is also hosted with www URLs i.e. www.google.com
But when you check their whois data, you will fill only their primary domain name i.e. non-www domain name. So, it is clear that www and non-www damains are considered as two different domain names or directories and hence it should be configured properly with the either one to make it one only.