Next week we'll automate the process more, but for now:
1) in your Steam library
2) right click on Nether
3) select 'Properties'
4) click 'Local Flies' tab
5) select 'Browse Local Files'
6) enter 'Game' folder
7) enter 'Binaries' folder
8) run launchnetherserver.exe
9) you will then be able to set up and run your server
You may need to forward ports 7777 and possibly 27015 UDP