Twenty Fourteen Theme configuration problem

Twenty Fourteen is attractive and simple theme, as shown in the preview of the Twenty Fourteen wordpress theme,the above shown featured post thumbnails are never there when we install it. Its a spam free wordpress Magazine theme, so i can trust this one and use in my site https://rox7.com , i tried all my best to figure it out. But still i wasn’t able to configure it. Please anyone help me and suggest how to get that featured thumbnail there.