@honeybeeblooms Express was built to just that EXPRESS so as little configuration as possible , be sure to first check out the other free themes that might be more suitable to setup longterm that come prebuilt with navigation. Express "menu" is literally intended to be the category options on one page, see the demo that has it for 'fresh meals',pasta,etc: https://express-theme-bistro.myshopify.com/
As for customizing express I mentioned it another post I made on this board but see the thread in the design forums for extended theme discussion to bring together the different customizations merchants might think they need. https://community.shopify.com/c/Shopify-Design/New-FREE-Shopify-Theme-Introducing-Express-a-theme-bu...
If you want feel free to visit that thread and detail as to what type of simple menu system your looking for, helps if you reference similar simple themes.
If you need a quicker solution there are many menu|navigation apps available