PActivityScheduler is responsible for managing a list of activities to be processed.
PActivityScheduler is given a chance to process these activities from the PRoot's ProcessInputs() method. Most users will not need to use the PActivityScheduler directly, instead you should look at:
PNode.AddActivity - to schedule a new activity
PActivity.Terminate - to terminate a running activity
PRoot.ProcessInputs - already calls processActivities for you.