hello, it is not difficult what you want to do. I have created with few steps a retro game server in docker.
If you have docker manager installed, just download the emulatorjs image and launch it with the default values.
To access the server administration you can do it through the browser with the address:
http://yournasip:3000
and to access the frontend
http://yournasip:37992
Then, follow the instructions of the web that you indicate in your previous post:
https://github.com/linuxserver/docker-emulatorjs/
And of course download some classic roms to load on the server.
Best regards
I hope everything works ok