When you run the Swift Calcs add-in, two options will be added to the 'Modify' menu and in the Fusion 360 Quick Access Toolbar.

Click the 'Load Swift Calcs' option to launch a web-browser.

Swift Calcs will be loaded in the browser, and only worksheets directly related to the current Fusion 360 document will be shown.

Create calculations and use the Swift Calcs 'fusion' toolbox option to sync answers in Swift Calcs with User Parameters.  Or sync directly from Fusion 360 using the 'sync' option that is added to the 'Modify' menu.

Install:

The installer that ran when you downloaded this app/plug-in from Autodesk App Store will start installing the app/plug-in. OR, simply double-click the downloaded installer to install the app/plugin.

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 Autodesk® Fusion 360™.

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 and Features' (Windows 7/8.1/10), just as you would uninstall any other application from your system.