What do you even search for once you've got your topic and research question solidified, or at least started? Well, you take the most important words in your research statement/question and use them as key terms. A key term may be a single word or a small group of words.
These key terms work for the Library Search as well as databases. Use those key terms in conjunction with each other (see the section on "Combining Key Terms" for advice about how to do so). Also, use synonyms of your key terms.