How do websites feasibly allow users profiles to each have their own URL?

Question

For example, a profile on facebook is often: facebook.com/user. What does Facebook do on their backend to make this work?

I want to create a similar experience for a site I'm building but I don't want to make every user their own .html page. I need some way to read the URL to determine which experience to serve

Answer 1

They don't serve static pages, instead they forward requests to a web application of some sort, which can handle URLs however it wants. You would also need to do that in order to handle use input, static pages obviously being static they can't handle anything.