For you to start forex trading with R 100 which I estimate to be around $5 you will need to trade with a high leverage forex broker probably 1:2000 type of leverage. Yes, this is high risk but when leverage is high, the margin you must deposit to open the trade becomes low and that is when R 100 will be enough to start trading forex.
Because you will be using high leverage it is likely you will be stopped out easily so you should set a loss limit and when your loss is up to that amount you close the trade.
I want to say that the reason why it is ideal to start forex trading with more than R 100 is so that you don't have to use so much leverage and put yourself at an elevated risk.
Now imagine you started forex trading with R2,000 you will be able to lower your leverage and still have enough money to cover your initial margin requirements. But when trading with a small amount like R100, high leverage is the only way to go and you can blow your account easily.