A Content Layout determines the manner in which a page's content will be displayed. To set a page's Content Layout, under Maintain/Web Categories, for the page in question, enter the name of the desired Content Layout in the "Layout" field of the Page Information tab.
Most layouts can display category and item lists in up to twelve (though no more than three to four are recommended) multiple columns, based on the "Display Columns" field as set on the layouts in System Management | Document Layouts.
Remember when viewing our samples that we are showing both Items and Categories on the page. When building your page you would normally just have one or the other.