Plugins are primarily used for connecting KeyShot with various modeling applications. Most plugins will be executed in the modeling application but some will be run from KeyShot (e.g. OnShape). The Plugin Preferences are only concerning plugins that executed inside KeyShot.
The Plugins window will show all installed KeyShot compatible plugins with checkboxes to enable or disable the plugin when KeyShot starts.
Plugins are installed via Windows or Mac OS X installation files and uninstalled through the operating system options.