Plugins listed here are automatically loaded when a world is opened, or a new world is created. This lets you have a list of "global" plugins (eg. the Chat plugin) that you always want to have available.
Add...
Click to add another plugin to the plugin list.
Remove
Click to remove the selected world from the plugin list.
Move Up
Click to move the selected plugin up the list (open it sooner).
Move Down
Click to move the selected plugin down the list (open it later).
Plugins Directory...
Click to select the default directory for loading/saving plugins.