Checks if your executable was launched through Steam and relaunches it through Steam if it wasn't this returns true then it starts the Steam client if required and launches your game again through it, and you should quit your process as soon as possible. This effectively runs steam://run/AppId so it may not relaunch the exact executable that called it, as it will always relaunch from the version installed in your Steam library folder/ Note that during development, when not launching via Steam, this might always return true.