Standard three-box search engine:
This example comes from Sociological Abstracts. Most article databases will have similar three-box search. This example illustrates a search on "college student's attitudes toward alcoholism" In this case, the database only display 2 boxes but additional lines can easily be added by clicking on... add a row.
And used to limit a search
AND produces results that include both terms
Example: treatment and recovery
Or used to broaden a search
OR Includes in the search each of the terms
Example: alcoholism or alcoholics
Not used to exclude terms
NOT will produce results that exclude a term
Example: NOT college students
produces results that do not include college students