Question about using express.js with nuxt.js (specifically with routing)

I'm building out a web app (mostly as an excuse to learn vue and get practice) and I'm currently using both express.js and nuxt.js

I'm hoping someone can walk me through the main differences between using nuxtlink routes for pages and using the express.Router() object (and when you would use one over the other).

My instinct is to use nuxt/nuxtlink routes for user navigation "front-end" stuff (like typical nav bar links to other pages).

I would use the express.Router() object for directing specific server requests outside of just GETting content delivered (like if I had to handle POST requests or if my web app also had or needed an API).

To be honest though, that's just a feeling I have. I'm still not positive what the difference is between what's happening under the hood, nor if it's a meaningful difference. I would really appreciate any help or links to good articles to read. I'm just having a hard time putting together where different parts of the stack/framework are being used. It seems like there is so much overlap...

Thanks in advance!