How to troubleshoot SSH Connection issues / SSH Connection Refused - Solved || Explained

The Story.....

We have two machines amazing-seasnail and first-shiner. first one being client and latter being server . ubuntu user on amazing-seasnail machine is configured connect to first-shiner . But due to some reason i am not able to do ssh login to first-shiner.

        I have tried to simulate few problems and how to go about in these situations and what could be possible causes

Here it goes ....... 

---

Thanks you guys !!

Have a great day ahead. Stay home stay safe, Keep learning keep  sharing .