You can find the dialog Scenes in the toolbar of the Animation Machine. However, at the moment, this is still a bit of a future prospect: An animation should be able to consist of more than one scene in the future, and then the transition will be defined at that point.

So far, you can specify in the dialog which timeline an animation should start with. This is necessary when a user action is not supposed to be the trigger for the animation.

The dialog lists the individual axes, and you can select the one that should be executed when loading the animation.