It looks like you're using Internet Explorer 11 or older. This website works best with modern browsers such as the latest versions of Chrome, Firefox, Safari, and Edge. If you continue with this browser, you may see unexpected results.
Keyword searching is essentially taking your best guess at the terms which will appear in articles that are about your topic. This can be a very effective way of searching. However, you may get a number of irrelevant results because the keywords you chose may appear in irrelevant articles. You also never know if you've found all the article on your topic.
Tip: The next time you're using a library catalogue/database or looking at a book or article, take note of the author defined keywords or keywords and subject headings used then try using those terms in your next search.