In this guide, I am going to explain how to create extensions by describing core extension entities and then creating a simple extension (you can download the example extension source code from GitHub).
You can also download extension template from GitHub.
When you create an extension, you have to export it to .JAR file and then add the file to your project using PETEP Wizard or by editing extensions.json configuration file.
If you create a useful extension, be sure to share it with the community on GitHub and send me a link, so I can promote it on this website.