Hello Rony,
In Web AppBuilder for ArcGIS you create a responsive web applications that you can run using a web browser. The app can be run on a desktop, tablet, or mobile, and it will adapt the screen size of the device.
You need first to deploy your app to a web server, have a look into the following link:
Deploy app—Web AppBuilder for ArcGIS (Developer Edition) | ArcGIS for Developers
If your intention is to build a native mobile app, then you need to build your app using AppStudio for ArcGIS .