Like other editors, you can add or remove global plugins from the Global Options/Plugins menu, or plugins that apply only to the active mud window's phonebook entry through the Window/Plugins menu.
You can load a new plugin from your local filesystem by clicking the file button.
The top list field in the Plugin editor allows you to select one of your existing plugins to review, edit, or delete. You can also select to Add a New plugin, which will permit you to enter enter one by hand, or click the build button to compose one based on your existing Global triggers, aliases, MXP elements, and timers.
When editing or creating a plugin, the first text area is for the plugin JSON definition, while the second text area is for the plugin JavaScript handling code. Consult the Plugin help for the proper syntax of the add plugin and javascript text areas. You can share your plugin work at any time using the download button to save the plugin json definition to your local filesystem.
When entering a plugin definition or the javascript code by hand, the appropriate text area will turn red and stay red until the document meets minimal requirements, or if it has any errors. When one of the text areas is red, you can hover over the little ? help button to the left of it to see the specific problem, or click on the help button to pull up the full help file.