Plug-in modules are software programs that add features to Adobe Illustrator. A number of special effects plug-ins come with your program and are automatically installed in the Plug-ins folder inside the Illustrator folder.
You can install any commercial plug-in designed for use with Photoshop or Illustrator. To install an Adobe Systems plug-in module, use the installer if one is provided. Otherwise, drag a copy of the module to the Plug-ins folder inside the Illustrator folder. Then restart Illustrator for the plug-in to take effect. To install a third-party plug-in module, follow the installation instructions that came with the plug-in module.