Before editing these you should make a file called server_info.cfg in your config files folder in the C:/program file/armagetron advanced dedicated/config/server_info.cfg. Put all the commands for the server info there so you won't have to repeat the commands in command line if you reboot your computer.
server_ip ipordnshere
The IP of the network hosting the server. If you are hosting I'd recommend using a Dynamic Name Server (DNS). It is actually required for some internet providers since your IP will change and that will mess up your server. You can get a free DNS at http://www.dyndns.org.
server_name namehere
The name of the server that shows in the server list.
server_port porthere
The port the server is on. I suggest using 4535.
message_of_day messagehere
When entering the server the message will show up before the player starts his round.
admin_pass passhere
Password for basic in-game admin.
max_clients numberhere
The number of people who can be on your server at once. This is useful for controlling lag.