From the 20th of October, all those aged between 12 and 17 years of age will be able to register for vaccination and attend vaccination sites to receive their vaccine.
To register you can use either a birth certificate, or ID if you are a South African citizen, or a passport if you are a foreign national.

Initially, those 12-17 years old could receive one dose of Pfizer vaccine. From 9 December, all children 12 years and older are eligible to receive 2 doses of Pfizer vaccine https://sacoronavirus.co.za/2021/12/09/circular-changes-to-vaccine-roll-out-eligibility-criteria-for-adolescents-12-17-years-09-dec-2021/