South Africa experiences a very varied climate, which depends on where in the country you are, and at what time of the year.
Taken region by region, the climate of south Africa is as follows. In the south-western Cape coastal area, the climate tends to be Mediterranean, in other words, hot summers and cold, rainy winters. Further up the west coast, temperatures tend to be relatively lower, due to the influence of the cold Benguela current that flows in the Atlantic Ocean there. On the east coast, however, the climate is subtropical, with hot, humid conditions around Durban. The northern interior, on the other hand, is a summer rainfall area, with cold dry winters and sporadic thunderstorms during the hot summer. The interior of the country is relatively dry, with sub-zero winter temperatures, as there is no regulating effect on the temperature caused by the distant oceans. The central northern region of the country is a desert.
A further note on temperatures. Temperatures in South Africa may be very different to what you are used to. “Cold” in South Africa is anything approaching zero degrees to a few degrees below zero. It never gets any colder than that, and it never gets that cold for any extended period of time. Summer time highs reach the mid-30s (in degrees Celsius) with the occasional day in the high 30s. It is rare for the temperature to top 40 degrees. Changes in temperature tend to be more extreme as you move away from the coast and the regulating effect of the ocean, since water changes temperature more slowly than land.
Generally speaking, you should respect the sun in South Africa. Try to avoid the sun between 10am and 3pm. Or, if you must be outside at that time, use a high factor sunblock cream and wear a hat. The summer sun in South Africa can give you a nasty case of sunburn, so take the necessary precautions.