Grid structure helps to easily customize structure by having a grid to place items on a page. For example, this box is grid 7, which makes the grid seven grids wide.
This box is grid 5, but a push command is used to push the grid over.
The boxes align and snap to grid postions, eliminating the need for constant readjustment. Push and pull may be used to place elements left or right on the screen. This grid is grid 10, push 2, which makes the box 10 grids wide, pushed over 2 grids.
Nathan Smith created the original 960 Grid system. Nathan Smith's grid was 12 grids wide with a total width of 960 pixels. My grid system is 15 grids wide with a total width of 1350 pixels.