Create a category called for example Animals. Then in this category create 3 subcategories: Cats, Dogs, Birds. Upload images to each of the categories. Go to Components/BP Gallery/Images. Click on Options button in upper right corner. Then click on Category tab and set Group images parameter to Yes. Change tab to Categories and make sure Subcategory Levels is set to at least 1 or All. Create new menu item of type: Category - Default, Category - Masonry or Category Squares depending of what layout you would like to use. In Category field select the category holding your subcategories (in our example Animals) and save this menu item. Now you should have a menu item showing Animals grouped by its category.