Normally traditional WP pages don't include categories, but if you're using an external plugin to add categories to your pages, these categories can be added as filter buttons for your grid with the following setup.
1. Install a plugin such as this one, and add some categories to your pages.
2. Holding down your keyboard's CTRL key, select both "Posts" and "Pages" as the "Post Types", and then select the categories that belong to your pages, and also choose the specific pages that will be included in your grid.
3. Visit your grid's "Nav-Filter-Sort" section, and add the "Filter" element to your grid's navigation WYSIWYG.
4. Staying inside the "Nav-Filter-Sort" tab, scroll to the bottom of the page, and you'll see the categories listed as "Available Filters".