If I do not have a steam controller (I want to use a PS4), how do I do step (4) - launch maplestory using your controller? Maybe I misunderstood the step.
Does this only work for wired controllers or can I use a Bluetooth dongle?
I personally play using a PS4 controller with the Bluetooth dongle as well. To launch a game using your controller you first need to be in Big Picture Mode. Follow step 3 to get into Big Picture Mode. Once you're in this mode you can use your controller to navigate the menus. Simply go into your Library and choose MapleStory from the list to launch it.