Still wondering on hostname

I have been looking through the many articles already posted on this and I still can’t quite understand it. I’ve setup things like MariaDB and another service and they both have pasted links that are weirdly typed and later I found out they used the hostname I have setup for my droplet which is (mydomain)Main. That’s how it’s setup.

So like when I connect remotely to MariaDB it will say weird things like http://(thathostname):3306 and I just went in manually to enter the IP address into BeaverDB. As well as the web service I have setup to help with monitoring and logging, it told me to connect to (hostname):(port) but they are not my domain and if I typed that in, it would of course give me an error because it’s not a TLD.

So what exactly should I use as my hostname? It’s a single domain droplet/site and no plans to ever have another domain lol.