Before you begin searching, think about your search strategy. Which words and phrases will you use as you create your searches?
Think about the topic you want to research. Write down your thesis statement or question, if you have one.
How can you summarize this topic into single words, or short phrases?
Think about related words and phrases. Think about words that mean the same thing as the words you've already written.
Use these words alone and combined in different ways to begin searching the databases. Keep an eye out for additional words and phrases you see along the way which might also get you to helpful information.
This video from USC San Bernadino does a great job at explaning what keywords are and how to think about them when searching.