I’ve answered you as well in this topic: https://support.redfactory.nl/forums/topic/adding-another-menu/
Regarding the creation of categories: Simply go to “Posts -> Categories” and create a new category. When you make your posts, you can add these posts to the categories you created 🙂
If you create a menucard, these categories are also the ones that you need to select to show up on the menucard.
If you have more questions about this, let me know 🙂