Looking to get code to add a forced sort by category in a specific order

We have a product gallery page that is displaying food menu items that are organized by categories and I’d like to have a single gallery page show all items but group them into sections based on their categoires. I would also like to sort them in a predefined order that I set. I have no expereince with code and don’t know if this is even possible. Any help and specific code examples would be much appreciated!!