Boolean AND is used to join together unique
terms or phrases when keyword searching.
The Boolean AND tells the database that each term is important, and
therefore, must be present in your search results. The more terms you
join with an AND, the narrower and more focused your results will become.
Boolean Logic is often represented visually using Venn diagrams.
In the above example the set of results are where the three circles
overlap. The search results would only include sources that contained
all three of the search terms.
By the way, you do not have to capitalize your Boolean operators.
capitalized merely for emphasis in the tutorial.