Even the simplest search engines have techniques for organizing the search, limiting the number of results, and fine-tuning. The basic search in Google is an "implied and": every new keyword is "anded" with the others. Google can do much more; use Google's Advanced Search link to see just how much.
The real problem for searchers is that it often seems like no two search engines use the same symbolism; the truncation symbol in Google is an asterisk; in Lexis/Nexis it's an exclamation point. Rather than memorizing confusing lists of symbols, rely on the Help functions in each search system; they will show what features are available and how to use them.
Many search systems automatically cluster (categorize) result sets. The system combs through the references, finding common subject headings, authors who publish a lot on the topic, journals that often feature articles on the subject, years where publications are plentiful or few... Search results can then be modified by clicking on appropriate links.
Logic
Truncation
Proximity
Many search services automatically truncate or find words near each other. This can be a problem when exact word order and spelling matter.