How do I use the checkboxes on the left side of my screen?

The checkboxes under "Refine Results" are used for filtering the results displayed on your screen. Initially, all checkboxes are selected and all results are displayed on the right. By unchecking a box, you remove all results that meet that criterion. For example, if you would like to remove all 1-stop flights from your consideration, you can uncheck "1-stop" and the results on the right side update automatically.