Katarina,
Don't worry. Look in the section on Research at groireland and you will see how the births are recorded in the register. With your father's full name, date and place of birth, there should be no difficulty in finding the correct registration and the certificate.
Uusally, researchers know the parents of the individual and are hoping to establish the date of birth.
There is also a tip about applying to the local Superintendant's Register Office for a quicker response.
To obtain a birth certificate from South Africa, you have to know the exact date of birth...
Good luck,
Justin