This report shows what type of operating systems your visitors are using. This is essential information for the design of your web site. Make sure that you create your pages using the same equipment as the majority of your visitors.
For example, if most of your visitors use Microsoft Explorer with Windows Vista, a 16 million colors screen and a resolution of 1024 x 768, then you need to look at your site under these conditions. Most likely you will be surprised by the result... Don't forget that you are designing your site for your visitors, not for yourself !