Open game folder like 'D:\SteamLibrary\steamapps\common\FortressCraft\64'
Launch file 'Dedicated Server.bat'
See the log. After loading you see IP address to connect. Do not close this window
Launch FC normally
Connect to your server IP
After client loading - you got it.
Invite your friends for more fun&achievements (you needed public IP).
To shutdown server write into server console 'exit' without quotes, press Enter and wait.