First of all, create your server from the Server Selection Window (the First window that opens up). After that, go to the “Software” box, and it shows custom. Click this, and select “Spigot”. From this, you can leave it at the most recent version, or select a different Minecraft Version. These are all supported, but may require different Java JDK’s to run.
After this, create the server. From this, a terminal will pop up. And it will start downloading the BuildTools.jar file provided by Spigot. After it downloads, it will start to compile the Minecraft version straight off your computer. This takes a while, so if your terminal doesn’t respond, just wait. CraftForge will not respond to any responses until this console closes. Don’t worry, it will automatically close once finished!
Known Issues (Not Bugs)
If Java is not installed, make sure to install the right Java JDK version. This can be found on this website, under the download button, which recommends a Java JDK. You can find the Download buttons on this page. I recommend restarting your computer, or else CraftForge may not initialise Java properly.
This can cause the application to instantly close and not install. Meaning the server tries to open, but cannot. And doesn’t show anything in the console. You will know this because it downloads the Spigot BuildTools.jar file and instantly closes.