Hi Billy,
The following steps should help you.
Step 1) Are you a HKID card holder? If yes proceed to step 2, if no then proceed to step 4.
Step 2) After submitting your application, be patient, wait, they will call you eventually if you are selected. Interviews are done on a regular basis.
Step 3) If selected they will call you then send you an e-mail to confirm what is to be expected on the interview date and what you should bring.
Step 4) You are not a HKID card holder or have failed their screening process and will not hear from them any time soon.
Best of luck.