add content of concepts/app-bue (#191)

Author: Mini-ghost

content/2.concepts/2.app-vue/index.md

@@ -4,8 +4,20 @@ ogImage: true
 
 # Application Entry
 
-To give you the full control of your application, Nuxt allows you to define your own application entry `app.vue` to start minimal (optional).
+In Nuxt, `app.vue` serves as the entry point of your application.
 
-// TODO:
+You can define a minimal `app.vue` to manage your application and begin implementing your own logic (optional).
+
+In this example, **`app.vue`** simply renders a message on the screen.
+
+The `pages/` directory, which will be introduced in the next chapter, is optional. If it does not exist, Nuxt will not include `vue-router` as a dependency.
+
+This is useful for landing pages or applications that do not require routing.
+
+Additionally, you can configure your application using `nuxt.config.ts` (it also supports `nuxt.config.js` and `nuxt.config.mjs`).
+
+By default, Nuxt is configured to cover most use cases, but you can override settings as needed.
+
+For more detailed configuration options, refer to the [Nuxt documentation](https://nuxt.com/docs/getting-started/configuration).
 
 To get more capabilities of your Nuxt app, let's continue with the [Routing](/concepts/routing) section to learn how we can make our app multi-page.