It seems you didn’t post a link to the exercise you solved. Can you please add it so I can have a look?
When you work through all HTML learning sections on MDN, I think, you’ll get a pretty good idea about how to structure a web site.
I think it’s important to first learn the basics of the technologies involved (HTML, CSS, JS). As you probably have already seen, these are covered in the various sections of the MDN learning area. Later you may want to learn a front-end framework like Vue.js, ReactJS or Angular. Such a framework will give you the ability to build more complex web apps like “single page applications” (SPA).