Mobile app Background Beginner

A beginner sees an interface and thinks it's not interface. But here is not, here is a URL,
The app passes the parameters to the URL, and then the URL returns the data to the app, and the app can then provide dynamic data with the server linkage.

For the simplest example, a user logs in.

A web system, the user through the browser to pass the user name password to the Web server, which is what you say backstage, then there is a URL such as called xxx\user\login.action?userid=zhangsan&pwd=123
You can then retrieve the UserID and PWD in the background and then return to the browser for success or not.
The same truth,
Android App Call xxx\user\login.action?userid=zhangsan&pwd=123
You can get both the UserID and the PWD in the background so you can return information to the Android app to tell him whether the login was successful or not.

So the so-called interface, is a URL,

Mobile app Background Beginner