Final answer:
The nurse will explain to the client that they need to self-administer the medication by pushing the button on the PCA system when they need it to manage their pain.
Step-by-step explanation:
The nurse will explain to the client that when they push the button on the PCA system, they will receive the medicine to manage their pain. The client must take an active role by self-administering the medication as needed. It is important for the nurse to emphasize that the medicine is not continuously flowing into their body and that they are in control of when they receive the medication.