This is quite straight-forward. Using absolute positioning, this column has its upper left corner placed 10 pixels down from the top of the document area of the browser and 10 pixels to the right of the left margin of that space. It sets a fixed width for the column, though as we will see, you could supply a relative value (such as a percentage) to create a stretchy layout that would keep the left column's width proportional to the document area's width.
Notice that this column is not able to be positioned. Its position will thus retain its "natural" place based on its location in the HTML file that generates the page. Margin settings ensure that the left and right columns (which are set to 200 pixels in width) will have room for their content without creating a visible space between any of the adjoining columns.
The right-hand column is so much like the left-hand column that it seems unworthy of comment.