Choose a number of columns for your grid and the space between the them (in percent) and click BUILD to create a fluid grid. Each column needs the .column class and another one for the width it needs to cover, for example .column-2. All columns must be wrapped in a .row div element.
After you've built your grid you will be able to see a preview of it with the generated styles and you can click the DOWNLOAD button to get a .css file with everything set.
