The grid has been a crucial tool in print design for over 100 years, but it has just become popular on the Internet in the last few. Grids are everywhere. The New York Times, Wired Magazine, and many other big websites are organized around a grid.
Grids are very useful for defining and separating information. They help guide the user through the design and make it easier for them to read. They also make a thinner column of text. Most lines of text should not exceed about 90 characters. Imagine how difficult reading a newspaper would be without columns.
Defining the grid
The grid is a system for laying out your design. It helps everything line up and makes the design look neat and professional. They look rigid, but grids are also extremely flexible. They can work in any number of columns to create as many different layouts as you can imagine.
In web pages grids are normally created with CSS. There are existing grid systems like the 960 Grid System (960 is a good page size since it is evenly divisible by 12, 16, and manyother useful numbers).
Grids work best when they are a guide and not a religion. Getting away from the grid when you have a good reason is art. Doing it without one is laziness.
Take a look at the websites you like. They probably have a grid. If you use Firefox then check out GridFox. It draws grids on top of any page.