neowin[.]net/news/public-testing-for-microsofts-project-xcloud-game-streaming-service-has-begun
thurrott[.]com/games/219630/project-xcloud-public-preview-is-now-live
thurrott[.]com/games/219637/first-impressions-project-xcloud-preview
xbox[.]com/en-US/xbox-game-streaming/
The idea is to play the games, including AAA, without having them installed in any way, using hardware in the cloud, or your Xbox rather than the CPU & GPU in the device you're using. It's starting with cell phones, but will expand to everything from your PC & laptop to tablets to smart TVs. The one hardware requirement [so far] is a Xbox compatible game controller with Bluetooth -- I'm guessing that USB controllers will [or can be made to] work with Windows PCs & laptops, when the service is available for those devices. As Thurrott points out, it's best to buy and use a clamp that will more-or-less mount your cell phone to the game controller [unless you have 3 hands etc.]. You'll also need an internet connection with loads of bandwidth.
As Neowin points out, invites are slowly rolling out -- Microsoft may be more interested in testing some phones vs. other makes/models. Next month [November] Google's competing service, Stadia is set to launch.
techradar[.]com/news/stadia-everything-you-need-to-know-about-googles-game-streaming-service