Encyclopedias, books, news sources, popular magazines, and search engines can lead you to articles that will be helpful in narrowing down your topic and finding additional keywords to search. When using an encyclopedia, read through the article's bibliography or references section to identify scholarly books and articles related to your topic.
You typically will not cite the sources you find as you begin your research. Use the background knowledge you build from these sources to develop your understanding of the language used by people discussing your topic. Add this vocabulary to a word bank you will use to search for credible and scholarly sources later on.
Use this stage of your research to get a sense for your topic in order to narrow your focus and formulate your thesis.