Next.js uses your folder structure as your routing system.
This can feel simple at first (“a folder becomes a URL”), but under the surface, file-based routing is one of the most expressive tools in modern web development.

In this chapter, we’ll take a calm, structured look at how routing works in the App Router, and how to use it to build clear, scalable, real-world applications.

No complicated abstractions — just practical, predictable patterns.

The App Router is one of the most important ideas in modern Next.js.
It replaces the old Pages Router with a more flexible, more intuitive, and more scalable way to structure your application.

Instead of thinking in terms of “pages with lifecycle functions,” you design your app in terms of composable layouts, nested routes, and Server/Client Components working together.

In this chapter, we’ll explore what the App Router is, why it matters, and how to use it without confusion or unnecessary complexity.