Right now you can create maps in Hammer, but you can't really add any functionality. You can't add doors, or buttons, or hurt triggers, and you can't add logic.
So now Scenes can be published and loaded as maps. Map projects can target specific games - which means that you can create maps using components that the game has programmed. And when you press play in the editor, you can play that scene in that game, straight away.
What's cool about this is that you can use ActionGraph to create a bunch of logic in your map, so you can have working doors and lightswitches, you can have death triggers, you can teleport the player around etc etc.
I'm testing this using Walker right now. So now in editor, you can create a new Walker Map - and it will create an addon project and give you a small scene showing you how do to some stuff. I'm no mapper, but I made an example map and published it here - you can play it in game from the maps tab.
This leaves Hammer out in the cold a bit, because you can't do any of that stuff. Don't worry - it's our intention to get this right in the Scene system and then make it all work in Hammer too.
