Global Categories are used to map your Highwire Store categories to other feeds such as Bonanza.
Go to Catalog>Categories
Click the drop down menu to the right of your category and choose Edit Category
Click the Choose Global Category button
Navigate the category tree to find the category that best matches your Highwire store category and click the Choose Category button.
By default, sub-categories will inherit the parent category's Global Category unless you assign a different Global Category to the sub-category.