I downloaded the server files like you are supposed to and ran the ServerStart.bat file.
Cmd window pops up saying "ForgeDownloadURLNotFound" and something else.
How can I avoid this problem and start the server up?

Nevermind I found the solution. I downloaded Forge Installer (not the windows one) and the universal file from the HTML Document included on the Server files, copied those on the same folder and it started working.