The Echo Script Project is licensed under the MIT License. You may do what you want with the code, but we are not liable for any legal encounters you encounter.
To clone the repo on IntelliJ (recommended), see this https://www.jetbrains.com/help/idea/manage-projects-hosted-on-github.html.
After cloning, specify the path for your debug script in the run configuration args. Set it as the first argument.
An example script was provided by the EchoScript team to show you how our language works. Our documentation is available in the wiki.