Hello friends,

What Is WWW and NON-WWW..?

Technical Difference between WWW vs non-WWW. When you add www. in front of a site, it acts as a hostname which can help with flexibility with DNS, ability to restrict cookies when using multiple subdomains, and more. Whereas non-WWW domains also referred as naked domains do not have a technical advantage

There is no difference between www and non www URL. Google and other search engine crawls it as a same.

www.mdrahmatullah.com
https://mdrahmatullah.com
These are the duplicate copy of a same website. Google prioritize one, specially www but the user will get the same result after clicking both links. If you want, you can redirect it by solving Canonical Issue from Google Webmaster Tools.

This will be the best thing to run a SEO friendly website.

There is not any difference between www and non www site for user point of view but search engine (Google) crawler treat them as a duplicate copy of the website.
for example we have two ways to write a website

1. www.chicago-tow.com
2. chicago-tow.com

When a user will enter both site 1 and 2, it will show the same result to the user but when a search engine crawler (Google bot) will read these website it will treat both page as a copy of each other. This term will be treated as content duplicity.
To solve these problem we used to redirect the one site on second site. That is 2nd link will be redirected to the first link. Reverse is also possible but the standard URL format starts with www, so we redirect the non www URL to the www URL.

The www and non www versions are treated differently with one group of links pointing to each version of ..