"What can be used in place of all-purpose flour? I live in South Africa and here we normally get cake flour and bread flour, and sometimes self-rising flour, but not all-purpose flour, though many recipes call for it. What should I do for a substitution?"
First of all, here's an article that describes the difference between all-purpose flour, bread flour, cake flour and so on.
As it happens, you've identified one of the important issues in the world of baking. Professional bakers don't measure flour in cups — that's way too imprecise, and leaves room for all kinds of errors depending on whether the flour is scooped out, spooned out, sifted, unsifted, and so on. The only way of ensuring a recipe's accuracy is to measure the flour by weight.
So if you're making bread, hard rolls, pizza dough or other tough, crusty products, you'd probably want to use bread flour. A cup of all-purpose flour, sifted, will weigh about 125 grams. To convert a recipe that calls for all-purpose flour to bread flour, you'd simply weigh out 125 grams of bread flour for every cup of all-purpose flour the recipes requires.
Similarly, if you're making cakes, pies or pastries, you'd probably want to use cake flour or pastry flour. And again, just substitute 125 grams of cake flour for every cup of all-purpose flour the recipe calls for.
Read All About Flour and learn the difference between all-purpose flour, bread flour and cake flour in more detail. Here's another blog post about How to Measure Flour.