Download the Mednafen Netplay Server compiled for Windows here. Extract the server anywhere you'd like. To run the server, either run "run.bat", or drag and drop "standard.conf" onto "mednafen-server.exe". To have the server auto-run on start up, create a shortcut to "run.bat", and place it at "C:\Users\[Your Username]\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup". Once you have the server running, open mednafen and run "/connect localhost" to verify it works. Once the server is working, open Command Promt and run the command "ipconfig". Take note of your computers IP address for later.
To compile the netplay server on linux, run the following commands (replace apt with your distros package manager):
tar xf mednafen-server-0.5.2.tar.xz
sudo apt install build-essential
./configure && make && sudo make install
Once that is finished, the netplay server should be installed to your system. You won't need anything else provided in the archive anymore except standard.conf. You can delete everything else. To run the server, just use the command "mednafen-server standard.conf" in the same directory as the config file.
If you are hosting the server on your own personal hardware (old computer, old commerical server, etc.), then chances are you'll need to setup port forwarding in your router settings. Each router is different, but you can find info on your router at portforward.com and by searching the internet. The info you need to know is the internal IP address of your computer. Your port forward should be for TCP-UDP, with external address "*", internal address as your computers IP address, and both internal and external port as "4046". If your router asks for a name, you can use anything you find helpful. If you have trouble with this, feel free to ask for help in the Digimon Rumble Arena Discord server. If you are running the server on a rented VPS rather than your own physical hardware, then you'll need to allow mednafen-server through your software firewall on port 4046, if you are using a software firewall.
To verify you have your netplay server setup and working correctly, ask someone else to connect to it from the internet. Someone in the Digimon Rumble Arena Discord server should be willing to help with this. Once this is working, you can ask Yuri Bacon#0423 to add a subdomain for your server. You'll likely get [your username].yuribacon.com, and everyone will be able to use that to connect to your server.