Choose a folder location to install the Minecraft server to. I suggest.

%homedrive%%homepath%\Minecraft

Download

Server

https://mcversions.net/

https://getbukkit.org/craftbukkit

From the folder with the two java files assuming you have downloaded version 1.12.1 for both Minecraft and CraftBukkit

java -Xms3072M -Xmx4096M -jar craftbukkit-1.12.1.jar nogui

On first launch the app will close. It will create a number of files. Edit the file eula.txt

eula=true

Once the file has been change launch Minecraft again.