This is the first step and the starting point for your research. You don't need to have a specific research question in mind at this point – just a general topic that you want to explore. Make sure to choose something that interests you, that you are curious about, and that is relevant to your assignment.
Once you have decided on a topic, do background research. It will give you a good understanding of the scope of your topic: subtopics, key issues, etc. It will also help narrow your focus. It's possible that not a lot has been written on your topic, if that's the case, you can always choose another one.
To learn more, watch the short video below (create by the NCSU Libraries).