When you add a Global Automatic activity Studio creates a PBL-Method and associates it to the Global Automatic activity. This PBL-Method contains the logic of the activity.
If the type of the Global Automatic activity is Execute when an event occurs, then Studio creates two PBL-Methods. One method has the same name of the activity and the remaining one has the suffix "_Listening". The Engine runs the first method when it starts-up or when you deploy the process. This method creates the listening component. When the event occurs it triggers the method with the "_Listening" suffix.
You should add Automatic activities in automatic role lanes. You can add Automatic activities in user-defined roles but this does not add any information to the process. The engine runs Automatic activities without the user's intervention.
The PBL-Method associated to Global Automatic activity can access predefined and local variables.
There are no transitions to or from the Global Automatic activity.