Search engines don't want us to think too hard about how we are searching. We type in our question and sometimes we find information that seems to match the question.
That's nice, but it doesn't always work and we're left wondering (and frustrated). Unfortunately, the algorithms used by search engines are proprietary (trade secrets). We don't really know exactly how they are processing our search terms -- when they work and when they don't.
The Library Catalog, Advanced Search, and the library databases, process words and phrases connected by "operators." The operators are the terms AND, OR, NOT. The terms are matched to titles, to summaries of the books, tables-of-contents, and sometimes to the full-text of the book. That's how it works. No secrets.
climate change [as a phrase]
narrows your search to find books with both the phrase, climate change, and the term, technology, in the description.
[or] global warming
broadens your search to find books with either of these phrases in the description.
In addition, most catalogs, and many databases, include subject headings or descriptor terms in the record that will lead us to other sources.