All the text in this column is in a table 425 pixels wide. That is why the text does not run from edge to edge of the browser window. Table borders are ugly. Luckily, they can be set to zero so that the grid structure of a table can be used without the lines. Design on the Grid Breaking up each page into an evenly spaced grid can help tremendously in laying out information.
Images span one, two or all three columns.
This is a basic idea of how designing on a grid can work. Web pages don't really work in four column layout. When reading a newspaper skipping to the next column or to another page is not a problem. Scrolling up and down a web page several times would be annoying. Still, using a grid system to place a column of text in opposition to images can reduce visual noise.