Displacement refers to being able to communicate an idea that is not present in time or space (in this instance, the word or concept for "later").
As the passage implies, displacement is mostly a human language feature. However, it has been observed in bees, which perform a sort of dance that indicates the location of flowers.
Role is simply what they are playing or acting. But the responsibilities are the role's doing action which means if teacher is a role she has a responsibility to teach well for student and make them to get good marks.
