In databases, you can search or combine any keywords related to your area of interest. These can be people, places, ideas, or anything that you might hope to find in the title, author, and subject fields of a book. For example, "Calvin" and "Geneva" would be a great search. "Calvin" and "Institutes" might help you find both a copy of Calvin's institutes, as well as any books about Calvin's Institutes.
Try multiple synonyms for your keywords, if possible, especially as professional jargon changes over time. For example, "priest," "pastor," "minister," "clergy," have all been used to describe similar roles over time. It's worth the effort to try several or all of these as needed.
Be careful with first names or English translations. For example, searching "Calvin" alone will give you more results than either searching "John Calvin" or "Jean Calvin." Further, not all books or articles list the full author name. Some citation styles in particular prefer to abbreviate the first name to just an initial "J. Calvin."
You can search multiple words with the same root by adding * to the root. Example: "Methodis*" would search both "Methodist," and "Methodism."
The asterisk (*) serves as a wildcard, so you can also use it to replace one or more letters within a word, in order to search multiple spellings of a word. Example: "Encyclop*dia" would search items with both spellings "encyclopedia" and "encyclopaedia."
For titles or other exact phrases, you can group words in quotation marks so that they are searched together in that specific order. Example: "United Methodist Church."