Keywords are simply those words you type into the search box to get the results you want. Just like in Google, you don't type your whole question, just the important words or terms that will help you get the answers. You must remember to treat the search engine like a computer. Use nouns (people, places, things, ideas) instead of verbs (actions). Verbs and adjectives (descriptors) are about relationships between things and search engines don't understand that.
This video will walk you through a few different keyword strategies as well as explain why keywords are important and how we'll use them to search.