How was Africa colonized?
Depends on what you mean.
Do you mean by humans at all, or do you mean when white people started colonizing and taking land on it?
Anyways, I can answer both.
The human race arosed in Africa, we all come from there. Everyone.
Everyone in Europe, North America, South America, Australia, Asia...
In Africa we evolved into the humans we are today. Then for some reason we migrated to other places, and now we are everywhere.
Though, if you mean the other thing...
Countries like England, France, Portugal, Spain, etc, were colonizing islands and continents. So they also colonized Africa. They also took resources home, and made the indigenous people into slaves.