Server on here are written in the programming language Java. In order to run and write Java you need a Java Development Kit (JDK). Download it.

Eclipse is an Integrated Development Environment (IDE). This is used to write, edit, and compile Java with ease. To run almost every server on here you need Eclipse or know how to use the command line Java commands. Eclipse makes your life way easier.

Once you figure out how to use eclipse, it's as simple as importing a Java project and clicking run. Youtube Eclipse initial setup if you get stuck. Good luck.