The Windows Sandbox is a Windows 10 virtual machine that can be quickly launched so you can test downloaded programs,browsers extensions, and suspect sites without risk of infecting your normal Windows operating system. The Sandbox has no effect on anything you try on your normal computer. It is great, but could be better, which we will discuss at the end of the article. To use it, you can easily transfer files that you want to be tested or copy text to and from its clipboard.
Source: https://www.bleepingcomputer.com/news/microsoft/using-the-windows-sandbox-to-stay-safe-online/