This page from MIT Libraries outlines several different considerations to keep in mind while searching databases. These considerations include: Boolean operators, truncation, keywords vs. subjects, fields, phrases, and stop words.
This handout from North Kentucky University outlines the differences between subject and keyword searching.
This tutorial from Colorado State University Libraries explains to users how to use Boolean logic (AND, OR, NOT) to construct effective search queries.
This web page from the University of Alaska - Fairbanks concisely outlines what Boolean searching is and how it can be of use to you.