Wallace and Kinahan's History of Namibia and Patricia Hayes, ed., Namibia Under South African Rule, 1915-46, are both worth consulting for your interests.

In a nutshell, what you need to know is that the mandate status of Southwest Africa put it into a strange position vis-a-vis South Africa's domestic policies. In the period before 1948, segregationist policy in South Africa itself slowly intensified but to a significant extent, the administrative policies followed by the Union of South Africa in rural areas predominantly inhabited by various indigenous African communities resembled the basic administrative structures of British and French "indirect rule" elsewhere on the continent. The difference here was that South African authority allowed a more substantial (but not particularly large) number of white, mostly Afrikaans-speaking, farmers to acquire land previously held by Africans in the territory.

The more extreme version of these policies established by the apartheid regime after 1948 posed a bit of a conundrum (but only a bit) to the apartheid state. On one hand, apartheid was an intensely, almost fetishistically, legalistic regime. (This was one of the basic reasons for international opposition to apartheid: it was one thing to have an illiberal society with regard to racial segregation and inequality, and another thing to deliberately intensify and extend racial inequality through the instrument of law.) So in particular, one of the major aspects of "grand apartheid" was the establishment of allegedly independent "homelands" within South Africa that were supposed to be the only "legitimate" country that most Africans could be residents and citizens of, with the fiction that they were only visiting migrants working in South Africa who would return to their real countries once they stopped working. The apartheid state at its height pursued this laughable (and destructive) fiction to great lengths, installing phony 'rulers' and their administrations in the homelands, creating border crossings and requiring travel documents, etc.

This created a bit of a weird situation when extended to Namibia, however, in that South Africa did not really have authority under the mandate to create the same kind of fictively 'autonomous' homelands within South West Africa. So the administrative structures it employed there were more conventional "reserves" of the kind used in many colonial states in sub-Saharan Africa. There was some flailing about how they were self-governing, but not as elaborately as in South Africa itself. Moreover, the white population of South West Africa was smaller, and the security environment was structured by somewhat different imperatives (primarily the "border war" that involved the Caprivi Strip and the border with Angola, but also concern to prevent joint operations between the ANC and SWAPO). Inasmuch as they could, however, South Africa imported most of its standard apartheid policies--pass laws, spatial segregation, segregation of public facilities, etc.-- over to its administration of South West Africa for the bulk of the period between 1948 and 1988.