Basic Setup
Include the border-box rule at the top of your css file to target all the elements. Border-box is a great way of controlling margins and padding within containers and divs. If you're interested in learning more about why this piece of code is usefull check out Paul Irish's article explaing the benefits of applying this rule to your css.
To seperate your column rows insert your grid columns inside a containing row. The class name is really up to you. Use the cleafix hack developed by Nicolas Gallagher when you add additional rows to clear collapsing floats. The clearfix is an effective way to keep your floating divs in the normal flow of the page layout.
In this example, a column name begins with .col_ followed by the column span number. Your column names can use other naming conventions like .span_col_1 if you prefer.