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.