Open with text editor and change options in file gameServer.properties:
serverListeningAddress - server IP address.
Internal IP address if game will be played through local network (e.g. 192.168.2.1). External IP address if game will be played through Internet (e.g. 22.214.171.124).
serverListeningPort - server port.
Make sure to allow connections in Firewall through this port.
useUdpConnection - determines if messages will be send using UDP or TCP connection.
UDP means faster communication but it may cause some packets lose. It takes true for UDP or false for TCP
Run server with the following command: java -jar SC23gameServer.jar
Steps to connect with own server:
In create new online game with friends screen you have to set Server as Private
In IP Address field put serverListeningAddress and serverListeningPort separated with colon char (e.g. 192.168.2.1:40111)