[Honey]

Really a useful Tutorial. but i have a question. can we add any custom domain name which was not a registered domain on any other host provider sites. but we just make it to redirect to my vps IP. ?

Nope that's not how it works.

To make a domain redirect to your vps, you must buy it and then use your DNS registrar ( I use cloudflare ) to make it point to your vps.

Once you've done that, the domain will direct to your vps ip, If you further want it to direct to a specific folder this tutorial will help you out.

tl;dr nope