Start the program with the MagicRectangle command or the plugins area in the ribbon 

The plugin has two options

New

With this option, you will create a magic rectangle 

Existing

It will ask you to select one or more rectangles, once selected they will be processed by the plugin and you will be able to manipulate their vertices

The installer that ran when you downloaded this app/plug-in from the Autodesk App Store will start installing the app/plug-in. OR, simply double-click the downloaded installer to install the app/plugin. You may need to restart the Autodesk product to activate the app/plug-in. To uninstall this plug-in, exit the Autodesk product if you are currently running it, simply rerun the installer, and select the "Uninstall" button. OR, click Control Panel > Programs > Programs and Features (Windows 7/8.1/10/11) and uninstall as you would any other application from your system.