These terms enable combinations of words (i.e. your keywords) to be searched at one time with different results, depending on the Boolean Operator used. 

AND

• Using AND retrieves results containing both keywords (history AND America)
• This narrows your results and brings back fewer results because they most contain both keywords

OR

• Using OR retrieves results containing at least one of the terms (history OR past)
• As this is counter-intuitive to natural language that we use in everyday speech, if you get confused, consider this phrase: OR IS MORE

NOT

• Using not retrieves results answers containing one term but not the other (archives NOT newspapers)
• This is a good way to exclude terms that are coming up when you search, but do not relate to your topic

You have to let the computer know when you are searching for a phrase or else it will search your phrase as individual words that may or may not be adjacent in the text. 

A phrase is two or more words that need to be together in a particular order to make sense. 

For example, United States is a phrase. 

To tell the computer to search your words as a phrase, enclose the phrase in quotation marks. 

So, to search United States as a phrase, you would type "United States" into the search box.