What was it like? would different tribes/ethnicities often attempt to kill one another off? How cohesive was the multicultural society? How common were uprisings against the British/French/Belgians/Portuguese?
This is a very complicated question with massive regional variation across the continent. We do not tend to think of ethnicity operating in the same way during the precolonial/early colonial period as it does in the later colonial and postcolonial periods. To make a massive generalization, there were certainly conflicts between states and polities, but those polities tended not to be organized along ethnic lines (there are exceptions, of course; again, this is a very big question).
There were major uprisings against all major colonial powers at various stages. Maji-Maji, Mau Mau, the Bambatha Rebellion, the Cayor Rebellion under Lat Dior, etc etc. And of course all the wars that eventually lead to independence (in Angola, Mozambique, Algeria, Cameroon, among others).