Basically story mode is just that: telling the story of the game. But you can still enter commands to look around, and examine things etc. All story mode does at this point, is to “do the next thing” when you press the ENTER key without typing anything. I have seen players playing my game and occasionally switching to story mode to briefly let the game play itself when they got stuck.
Sorry to disappoint, but the story mode as I implemented it is not a standard feature of Inform7. It works for my IFComp entry because the player does not have complete freedom as is generally the case in parser games. The game is “story-forward”, driving the player onwards.