Scene Transitions define the animation of a scene entering and leaving on a device.
You can select from a number of options for both the transition in and out, as well as specifying the length of time a transition takes to complete and the delay before this transition starts.
The 'Transition In' effect occurs when a scene is navigated to and defines how it enters, whether from the scanning of a zapcode (as with the first scene in your experience), or when one scene navigates to another, such as when a button is pressed and the 'Go to scene' action is used.
The 'Transition Out' effect occurs when a scene is navigating to another scene and defines how the current scene leaves. For this reason the 'Transition Out' effect relies on a following scene and will not work with a single scene by itself.
For more information on Scene Transitions please see the Transitions tutorial video.