Joining the British army?

I am in South Africa, but I am British citizen. Im 16 turning 17, is there anything i need to join the army. We have government papers which like GCSE, we do them when were 16 same as uk but We carry on in high school until matriculation which like advance GCSE until age of 18 then comes college and university . Will I need any of this. Will I be able to continue education there?