Chances are that you've already done research for other classes, and now that you're working on your Capstone project, these skills may seem like second nature. But, it never hurts to have a refresher!
Finding relevant research articles is an important part of any research project, because it sets the stage for your own, original contribution to the literature. Usually, this research starts with a literature review, that can help you to identify what has already been explored about your topic, while also helping you to focus your own thoughts in order to write an informed final product!
In order to conduct a thorough literature review, you should generally look at a variety of resources, rather than focusing on just one or two. These can often include books and encyclopedias, scholarly articles and sometimes Internet resources (ALWAYS check with your professor before using these, though).