When first learning about a topic, you may wish to use background sources like encyclopedias, handbooks, almanacs, etc. to get a clearer idea of what you're looking for.
Look to your assignment to see what types of sources your professor is asking you to use. If you're already comfortable with a topic, you may wish to start looking for scholarly articles right away.
You can begin your research in any of these places. Remember different types of sources contain different kinds of information.