Before you dig deep on any research task, it's a good idea to build your general understanding of the subject. This will help you later when your start focusing the topic and writing your research question, as you'll have a better understanding of the issues around the topic, as well as the special vocabulary related to that topic.
This is where general databases and reference sources (and, yes, Wikipedia!) are useful; they give basic information about a topic--dates, facts, names--without overwhelming you with detail.
For DP classes and Extended Essay, it's usually better not to cite these as sources, unless it's for definitions. They don't include original research, just summaries, so just them for your own general knowledge.
Use the links to the right to start your information gathering.
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A note about Wikipedia.
Wikipedia is a great place to start doing background research, especially if you don't know much about the topic. However, because anyone can edit the pages, it is open to vandalism and thus not a totally reliable source. It is certainly not a source you can cite in an acedemic paper. So use it for background, but find better sources to cite!