To register for a card, you can make an appointment. You can also go in person at one of the five ‘Registration of Persons’ offices and join the queue to wait for as long as it takes. If you decide to visit one of the offices without an appointment, make sure you arrive early. Each office has a daily quota of people they will see and they could reach this before you are seen. The whole process may take an hour; all you need to take is your passport with a valid visa.
You do not have to pay a fee for your ID card (unless it is a replacement for a lost original). Once you have completed the forms, have been photographed and fingerprinted, you are issued a temporary identity receipt and a date on which the final card can be collected. If you cannot go in person on the allotted day, you can give a letter of authorisation to a HK ID holder along with the temporary ID receipt; they will then be able to collect it for you.
The Hong Kong ID card is valid for as long as you are resident in Hong Kong, and you should carry it with you when you go out. If you lose your card or it gets damaged, the replacement fee is HK$395.