I am a developer, who knows close to nothing about design, so please bear with me. As I read books about design, I keep getting stuck at the idea of a grid system such as 960gs. I completely understand designing within a width of 960px, but I don't understand what the red columns are for, or how this helps with the layout of a site. As a side note, I don't really see the benefit of the class library, as it just seems to increase load time for basic styles.