Keywords are the terms you use to search in the Libraries' databases. They distill your complex topic down into its most basic elements. You keywords should not be a sentence.
Keep in mind that you can try many different keywords and can always look for new ones -- when you find articles, books, or other resources, see what keywords the database uses to describe the article. If you're stuck, these new keywords can help you find more information.
If you are finding you get too many results (thousands) you may want to try adding a few more keywords to make your search more specific to a country, organization, or time period. Apply filters to restrict to certain kinds of results based on publication type, time period, etc. If you are not getting any results or only getting a handful of results, try using a fewer keywords, or try some broader terms.