1) press the heart while the game is running
2) select a scene to live edit from the opened scenes
3) edit/add/remove nodes or resources, change their properties, etc.
4) watch changes reflected in running game, in all places this scene is
edited
5) It's not perfect obviously, but the aim of it is to try to reflect
your changes as best as possible in the running game.
Juan Linietsky
George Marques