Install it and then you are ready to install the Windows Sandbox. When you have followed the guide, go to windows update and check if you see the Windows Insider Preview 18309 (see pic 1). If you have not started the microsoft insider just follow this guide You can sign up for insider from the link.

And you must be running Windows insider build 18305. So what do you need to test the new Window Sandbox? You need to run 64bit version of Windows 10 pro or enterprise. The user or developer won’t need to download a Windows iso or configure the virtual machine. Windows Sandbox is easier to start than Hyper-V virtual machines. When its closed, all the software and files and the state are deleted. Software installed inside the Windows Sandbox environment remains 'sandboxed' and runs separately from the host machine. And every time Windows Sandbox is started, you get a new clean installation of Windows, meaning no files and applications are preserved from the previous session. Windows Sandbox provides a lightweight desktop environment to safely run applications in isolation. So what is Windows Sandbox? The Windows Sandbox provides an isolated, temporary desktop where users can run and install applications that could do some unwanted changes to Windows. Windows Sandbox comes with Windows Insiders update for Windows 10, build 18305

Windows sandbox