You will need to download the SpigotMC server software (if you haven't already installed it) and ScriptCraft.
ScriptCraft must be used with SpigotMC (or CanaryMod though that is no longer in active development so SpigotMC is preferable). SpigotMC is a custom version of Minecraft Server that allows Server mods to be added.
You should save the SpigotMC Server Jar file on your computer. I recommend saving the file in a new directory called spigotmc. Once downloaded you can launch the SpigotMC Minecraft Server by typing 'java -jar spigotmc.jar' at a command prompt.
The first time you run SpigotMC it will stop immediately. You must edit the eula.txt file in the same directory and change the 'eula' property to true. After doing so, restart SpigotMC and it will proceed as normal.
Save the scriptcraft.jar file to the spigotmc/plugins directory, then restart SpigotMC.