Try this direct link if the embedded video above isn't working.
Once you know what you want to research, it's important to narrow down your topic. If your topic is too broad, you'll have too much information and won't be able to answer your question.
You can narrow down your topic by being specific about a specific aspect of the topic, a particular group of people, or a certain time period. Have a look at these links for more guidance on narrowing down your topic: