Press Shift+S in Fusion and go to the Add-Ins tab. Then select the add-in and click the Run button. Optionally select Run on Startup.

A warning will be shown every time a new feature is created at the top-level or in the wrong component.

At that point, the following choices are given:

• Cancel (Esc): Cancel the operation
• Continue (Enter): Go through with the operation and create the feature
• Stop warning: Go through with the operation and stop warning for this document for this session.

Install:

The installer that ran when you downloaded this app/plug-in from Autodesk App Store has already installed the app/plug-in. OR, simply double-click the MSI to install the app. 

Uninstall:

You can unload the add-in without uninstalling it by clicking the "Stop" button when the add-in is selected in the list box on the "Add-Ins" tab of the "Scripts and Add-Ins" dialog.

Unchecking "Run on Startup" causes the add-in not to be loaded in future sessions of Fusion.

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, you can uninstall it from 'Control Panel\Programs\Programs and Features' (Windows 10/11), just as you would uninstall any other application from your system.