Hi there,
Thank you for getting in touch with us.
The best way to do this is by adding selected category, not standard page to the menu under Appearance → Menus. When you click Categories tab in dropdown menu on the left you’ll see all categories. Then just add one of them to your menu. This is how “Desserts” or “Dinner” were added in Kale demo. They’re not standard pages but categories.
Hope that helps. Thank you for your time in this.