I've used it frequently both to and from EWR and it is pretty painless. You just follow the signs in your arrival terminal for the AirTrain, board the monorail to your right as you come up the escalator and depart at the AirTrain station. You can purchase your tickets at either Newark (at machines) or at the train station itself. At the Newark Airtrain stop you would take any train heading towards NYC (there will be lots of montiors displaying departure times and tracks. (It could be a NJ Transit or Amtrack train). The entire trip will be between 50 min and 1 hour.