Only those in the top three ranks are 'reachable' and ready for appointment. Even if you are in a lower rank, don't worry. Contact letters are sent to those that are reachable and ready for a job. Because the eligible list has more candidates than needed for the interview, there is a random computer selection program to choose the candidates that will receive a job inquiry. During this time you will receive training related to your position, and receive regular evaluations tracking how well you are doing on the job.
Most employees successfully pass the probationary period and become permanent staff.