Luna is the cloud gaming service from Amazon. If you have Amazon Prime, you have a small selection of games to choose from. If you pay for membership, you have a larger selection. Nothing is installed on your computer to play the games- it all works through a browser. If you use an Amazon Firestick, there's a dedicated app for it. All of the hardware is on Amazon cloud servers  they run the game and deliver the video feed to your browser.  As you can imagine, there's a bit of latency involved normally. Amazon runs the game, sends the video to your PC, you see action on screen and hit a button on your keyboard, which sends the action back to the server to execute. It can work with a Bluetooth controller connected to your PC, but that adds a bit of extra latency as Bluetooth has its own delay. A Luna controller connects to the Luna service directly via your wifi network to remove some of that latency. It's not required at all to enjoy gaming, but some people like the extra responsiveness. If your father wants to play on a fire stick instead of a browser, the controller may be necessary. Answer from retropyor on reddit.com