Before you can start any research on your topic, you must have a background knowledge of it. Books and websites can provide you with that knowledge.
This is important because:
Background sources give you the language that people are using to discuss your topic. You will use this language when you start to search databases for scholarly articles and resources on the topic.
This "pre-research" gives you a sense if your topic is focused enough. If your initial searches bring back so many results you can't even figure out what the language is, then you should consider narrowing your topic.
This is an example from the Political Science guide.