What the Function of PLUGIN ?

This the Screenshoot

#The Main Question :

1. What exactly main function of Plugin ?

I've download someone Template the name is "Gravity Zone", It's include 2 Folder .. Capx Folder for load the project & Plugin name "2D_Starfield".

2. Yeah I know the Plugin must be Copy in Program C2 ..

The Question is :

While Im not using this Plugin, the Project wont run without Plugin .. Why ? Its very Important >_< ? Im looking tutorial in Youtube how to make Gravity Zone, Many Tutorial working good without making plugin or load plugin just need the Code .. So What the plugin & Its Important ??

Plugins are extensions to Construct and allow additional functionality. The project you refer to uses this plugin and will not work without it being included. Not all projects need plugins, but if you use a plugin it requires it. Otherwise, Construct won't know what you are referencing.

Think of it like a car battery. You can have a car without a battery, but it won't start without one. The battery is a plugin to the car to add functionality. Without it, it is just a cool vehicle you can sit in.