Just choose which country you want and click the button. Pick whichever location is closest to you, or actually closest to where the content or service you are reaching sits -- for most people that is the same thing, but it is not always, and the account works the same regardless of which one you choose.
Xray is a maintained fork of V2Ray with a faster core and newer transports. This is Vless carried over WebSocket by Xray: the client configuration is the same one V2Ray uses, the server behind it is not.