I've heard that humans originated from Africa. Ok, then what? How did they get to all the other places? Is this a specific branch of study? Where can I learn about this?
The early human migration would be a good topic to ask about in /r/AskAnthropology, since the written record began much later after that.
Interdisciplinary stuff, involving archaeology, anthropology, and a lot of more recent developments comes from genetic research (arch[a]eogenetics / genetic history / population genetics). There were quite a few popular histories in the early to mid 00s (e.g. by Bryan Sykes, Luca Cavalli-Sforza, Stephen Oppenheimer) but these have been superseded and I haven't so far been able to find good recent equivalents. (There is A Brief History of Everyone Who Ever Lived by Adam Rutherford, but a detailed Amazon review pointing out various errors or assertions of unresolved and controversial points as fact makes me a little wary of recommending it.) There is still a lot of research going on tweaking findings as more populations are tested and maps redrawn, and a lot of this stuff is in journal papers (and then reported on sites like sciencedaily). For example: http://www.nature.com/news/african-genes-tracked-back-1.13607
In archaeology, very recent findings may push back the arrival of humans in Australia another 15000 years: http://www.nature.com/nature/journal/v547/n7663/full/nature22968.html?foxtrotcallback=true
Basic overview, but this stuff is always subject to updating as above: https://genographic.nationalgeographic.com/human-journey/