You can use the Internet to learn more about the Kongo people, their history, and their culture.

The Story of Africa: Kongo
The BBC World Service takes an in-depth look at the history of Africa and interactions between its inhabitants and Europeans. This page focuses on Kongo. From it you can link to pages on trading and on the arrival of the Portuguese. You can also listen to a broadcast on Central Africa & The Coming of the Portuguese, which tells the story Zimbabwe and Kongo at the time of Portuguese contact and colonization.
http://www.bbc.co.uk/worldservice/africa/features/storyofafrica/10chapter2.shtml