Specify Cache Validators for a Beginner

When running my page through GTMetrix (page speed analysis) I get a low score on specifying cache validators. It gives me a long list of things that are apparently missing a cache validator. I’m a beginner so all the help I’ve seen is too complicated for me. I think I tried one simple tip but it didn’t work. How do I specify cache validators? If you need it, my URL is http://www.livelaughandplay.com