To find as much good information on your topic as possible, you need to break it down into keywords. Keywords are words and phrases (including names, dates, and subjects) that describe the parts of your topic.
Say you are doing a research project about how immigration to the U.S. from Mexico affects families.
From this topic idea, we have the following keywords:
These are words that you will use to create your search string. A search string is one or more keywords, linked together with AND or OR, that you will use to search the library databases.
However, there is more than one way to express your topic. Each of those keywords has synonyms. It is important to make a list of as many synonyms as you can think of for each of your original keywords, so that you can make your search string as comprehensive as possible.
For example, your original search string might be
immigration AND families AND Mexic*
Here is an example list of synonyms:
At this point, you might also realize that you are really interested in the psychology of mothers whose children have immigrated to the United States from Mexico. The word "psychology" would then be added to your list of keywords.