I'm a South African, and I'd always hear my parents and other adults talk about the war in Angola as something very important that happened and that is was a big focus point during the Cold War and that many countries were involved in it.
I'd like to know why did a war specifically start in Angola(not a well-known country in my opinion) and why were so many countries involved? I can understand why the USSR and USA were involved, but why Cuba and specifically South Africa? And what happened at Cuito Cuanavale that made it so important?
At the time of the conflict in Angola, S. Africa claimed what is now Namibia, and the rebels who were fighting for the independence of "SW Africa" operated at least in part along the SWAf-Angola border. So the conflict actually started inside S. Africa (or at least inside they borders it claimed), and then fused into a broader war that included Angola.
During the period after the success of the Cuban revolution, the former revolutionaries continued to offer training to many other third world revolutionary groups, both in Latin America and in Africa. The initial aid to the MPLA took the form of military advisors.
Sorry if these are not as detailed as you were hoping for - I realize I didn't explain why Cuban/S. African involvement attained to high troop levels it eventually did, but your question seems to imply you didn't know the basics of how these countries became involved, which I hope I've clarified.
I think this is a strong post to answer your questions:
http://www.reddit.com/r/AskHistorians/comments/ygwub/cuba_and_angola_1970s/