I NEED HELP SETTING PRODUCT CATEGORIES ON MY SHOPIFY SITE

I am seeking assistance in organizing product categories for my Shopify store, which specializes in garage doors. The task involves establishing product categories and managing size inventories effectively. For instance, under our white door category, we offer four different sizes, and I need to ensure that each product is represented correctly with its respective sizes. This setup will allow me to list the items and upload photos seamlessly. Your expertise in Shopify configurations will be invaluable in streamlining this process and enhancing my online store's functionality.