Keyword searching with one or a few natural language terms is a great way to start your research. It's flexible and forgiving. The challenge may be that the search can yield too few, too many, or a certain number of irrelevant, out of context results. However, a good keyword search can also find great results and lead to good subject headings!
Hint: try using the advanced search page, if one exists, in any database or search tool, to help you build your keyword search. Or, try these kinds of approaches in any basic search box too:
"pride and prejudice" and femini* (* finds feminism, feminist, feminine... )
jane austen and (conduct OR manners) (finds jane austen and conduct, or jane austen and manners, or jane austen and both conduct and manners)
Subject headings or pre-defined "controlled vocabulary" terms or phrases are assigned to every book or article you find in NUsearch or a particular database. A challenge can be that you have to know that vocabulary before you can search on it. However, once you find those important headings (sometimes called descriptors), your results can be extremely relevant. In addition, you can narrow down to sub-headings or sometimes even jump to broader or related subjects to the one you have found.
Examples of subject headings in NUsearch:
Try using the Advanced Search in NUsearch, and search under the Books tab only, to narrow down and gain more control over the initial search.