Keywords are the words you use to search and they determine how successful your search is. If you are researching the effects between pesticide usage and cancer in children, for instance, the most important keywords would be: pesticide, cancer, children.
Generally, it is recommended to only enter 2-4 essential keywords. Do not enter a complete sentence as your search phrase.
Here is an exercise to help you generate keywords:
We will go into further depth on developing keywords by using a concept chart in Chapter 3.
This video from McMaster Libraries explains how to choose keywords for database searching when doing research.