I feel a little guilty posting this here. Jacob is busy creating far more polished video tutorials at the moment, however, this is in response to specific questions on the Steam forums here.
A-Train 9 allows the user to create their own scenarios, and the editor which allows this uses many of the same game navigation elements as playing the game does. So if you want to place a building in the editor mode, you do exactly the same as you would in game. The difference being that their is no cost involved, and unless you set it otherwise, whatever you place belongs to the AI once a game is started.